I host a weekly Gamenight, and I usually arrive arms laden with games of all shapes and sizes.  Planning game nights in advance allows me to fill a large duffel bag with a wide assortment of different games, drive down to the bar and distribute them to those assembled.  My reputation as the local "Game Guy" has gotten around, though, and I will often wind up at a pub or a social event emptyhanded and my friends will ask if I brought anything we can play.

This started happening so frequently that I would often carry a current favorite around with me.  But we could only play it if we had the right number of people, and if everyone liked that particular type of game. My solution to this problem was to consolidate a whole host of small games into a single box -- an all-purpose Emergency Gaming Kit.  In this way I could be prepared for every occasion, be it a a small gathering of gamers or a large group of party game enthusiasts.

At any given time my EGK contains a few decks of cards, a bunch of dice, pencils, paper, and maybe some poker chips.  Here are 15 of the games that you may also find inside.  All have the advantage of being portable, and most are relatively light in nature so they can be taught on the fly.  The exact composition of the EGK changes all the time, but here are some of the staples. (Note the "essential components" marked with a * are, in fact, not essential. That makes perfect sense, doesn't it?)
 

En Garde
Players:  Two
Type: Card
Essential components:  31 cards, four dice
Play:  One of Reiner Knizia's earlier games and probably his smallest.  Seven of the cards are laid end to end to form the fencing "piste" which has 23 spaces; the other 25 are used for play, five cards in each of the rankings 1-5.  Each player puts his fencer (represented by a die) on his end of the piste, and may play cards to move him a corresponding number of spaces forwards or backwards.  When someone plays a card that would move his fencer into the space occupied by the opponent, he is attacking.  The attacked fencer can retreat, or parry by playing a like-valued card.  With only 25 cards in the deck it's relatively simple to keep track of which cards have been played, so the gist of the game involves getting your fencer in position and then attacking with an unstoppable card.  Elegant and exciting, a game takes less than 15 minutes to play and the rules take about 90 seconds to explain.  Plus, the only game I know of recommended by the German Fencing Association!

Lost Cities
Players: Two
Type:  Card
Essential components: Deck of 60 oversized cards
Play:  The size of the cards almost rules this one out, but it's such a good game that I usually bring it along anyhow.  Players strive to mount expedition to find five "lost" cities.  A player receives points based on the number and value of the cards he plays for each city.:  But each Expedition also costs 20 points, so if a expedition comes up short he may lose points for his effort.  A fantastic game, with plenty of strategic choices to be made.  The game comes bundled with a game board, but it is wholly unnecessary to play; just form the discard piles on the table between the two players.
 

Button Men
Players:  Two
Type:  Dice
Essential components:  Two buttons, about a dozen polyhedral dice
Play:  A "mean little dice game for two"  from Cheapass Games.  You and your opponent roll five dice, and you attempt to capture your rival's dice by using Power Attacks (taking one of his dice with a higher die of your own) or Skill Attacks (totaling two or more of your dice to exactly equal the value of one of his dice).  When someone loses all of their dice, each player earns full points for the dice they captured from their opponent, and half points for each of their own dice they managed to retain.  The person with the highest score wins the match, and winning two matches makes you the champion.   Plays in about 5 minutes, an there are plenty of buttons to choose from.
 

Verrater
Players: 3-4
Type: Card / war
Essential components:  Deck of 80 cards
Play:  Before I assembled my Gaming Kit, I used to just carry Verrater around in the breast pocket of my coat.  The producers of Verrater could have just as easily marketed this as a board game, but instead you start each game by assembling the "board" by laying out 12 territory cards.  The game concerns the war of rival houses (the Rose and the Eagle), each striving to take over the other's land.  Players will belong to one house or the other, but as the translated name of the game ("Traitor!") indicates, switching sides is common.  During the course of each battle, each family plays supply cards to bolster their side's total, and the highest total wins.  And a clever scoring system keeps everything in balance.  Verrater is the one game that has a permanent spot in my kit, both because of its exceptionally small size and its exceptionally high quality.
 

Buried Treasure
Players: 2-4
Type: Card
Essential components: Deck of 76 cards
Play:  The American rerelease of Sid Sackson's " Das Super-Blatt", this game is so light and simple that I can't understand why it's fun at all.  Players take cards from a central tableau and try and collect the most in four suits.  But some cards allow the player to do other stuff, like take additional cards or steal from an opponent.  The trick is to get the card you need off the tableau without freeing up the special cards for the other players to plunder.  Lots of reversals of fortune in this one, which make it great family fare.  Plus, the rules can be explained in a single breath, and you can plow through a game in about 20 minutes.

Schnappchen Jagd (Bargain Hunter)
Players:  3-4
Type: Card / trick-taking
Essential components: 110 cards
Play:  This earns a spot in the box because it's just about the best three-player card game around.  There are nine types of appliances in the game, but each person only considers one category to be a bargain: cards of that type are added to his bargain pile, all the rest go to his junk pile.  Players can switch bargains from one round to the next, and possibly convert some of their "junk" into gold.  The problem is, as in real-life bargain hunts, there's always more junk than there is desirable goods.  At the end of the game the players will score one point for every bargain they accumulated, but will also lose one point for every junk card they took.  It may look like a routine trick-taking game, but Schnappchen Jagd will surprise you with its innovative mechanisms.

Bohnanza
Players:  3-5
Type: Card / trading
Essential components:  110 cards
Play:  Is Bohnanza the best card game ever?  Many of my friends think so, and I'm certainly willing to be convinced.  Players plant, harvest and sell eight varieties of beans in the hopes of making the most money.  Everyone gets dealt random cards, though, so to get the beans you want you'll have to trade and negotiate with your fellow farmers.  In many respects Bohnanza feels like the trading aspect of Settlers of Catan in compact, card game form, but it's also got a flavor all it's own.  Bohnanza is probably the game I have most given to people as birthday and Christmas gifts -- let that tell all.

Modern Art
Players:  3-5
Type: Auction
Essential components:  70 oversized cards, 88 small plastic coins, game board, 5 visors*
Play:  It's billed as a board game, but the heart of Modern Art is the deck of 70 Art Cards.  The cards belong to five artists (suits), and each turn one of these cards it put up for auction where all players can bid on it.  At the end of each round, the paintings of the most popular artist appreciates the greatest in value, while other artists painting may appreciate to a lesser extent or wind up worthless.  Players can make money either by selling painting to other players, or by purchasing other's paintings and hoping the artist turns out to be a wunderkind.  A bit dry for my tastes, but Modern Art can be enjoyed by both a group of causal players or a group of serious gamers (although a mix of the two can get frustrating, as some buy logically and others buy on a lark).

Illuminati
Players:  4-6
Type: Negotiation / "mean"
Essential components: 106 cards, two dice, a bunch of tiny "money counters"
Play:  It's your ticket to world domination and it only takes up about six square inches.  Illuminati is so portable that I actually took it to the Peace Corps with me and carried it around for a couple of years straight.  Everyone takes the role of a Secret Society, which infiltrates various groups and organizations, ranging from the Boy Scouts to the KGB.  If you're not strong enough to take over a group outright, you can spend money to bolster your attack.  But here's the bad news:  your opponents can also spend money to thwart your plans.  If anyone bothers you too much, you always have the option to attack them directly. A great game, but only play it with really good friends or people who are already your enemy.
 

Call My Bluff
Players: 3-6
Type: Dice / bluff
Essential components:  Five dice per person, game board*, dice cups*
Play:  If you've ever played Liar's Dice you already know this game.  Everyone rolls five dice, but hides them from view from their opponents.  Each person, in turn,  must then bid, or challenge.  To bid, you state how many dice of a given number you think there are in total, like "seven 5s".  Or you can challenge someone else's bid, and see if they were right.  If the bidder is correct, the challenger loses dice; otherwise the bidder must give up some dice.  Last person with dice wins.  Easy to teach and playable in 15 minutes, it goes great with a pitcher of beer or two.  The full game of Call My Bluff comes complete with dice, dice cups and a handy board, but all you really really need are the dice. 

The Great Dalmuti
Players: 4-7
Type: Card / "mean"
Essential components:  Deck of 116 cards
Play:  This quintisential "bar game" is a proprietary version of the old game "Presidents" (aka Asshole).  The cards are ranked from 13 to 1, and each rank contains a number of cards equal to it's value (so there are thirteen 13s, eight 8s, and a single 1).  Someone leads one or more cards to the center of the table, and each other person must either play an like number of cards of a better (i.e. lower) rank, or pass.  When everyone has passed, the person who played last leads the next round.  Play continues until everyone has gotten rid of all their cards, and then everyone changes seats, with the person who went out first as the "Great Dalmuti", the person who went out second as the "Lesser Dalmuti", and so one, all the way down to the lowly "Lesser Peon".  A fun game amongst friends, doubly so if everyone plays up their roles.

Corruption
Players:  4-7
Type: Card / bluff
Essential components:  Deck of 90 cards
Play:  Six Contacts are put up for bid.  Each player starts with six Bribe Cards (ranging from $1,000 to $10,000), a Hit Man, A District Attorney and two reports.  players take turns putting these cards on one of the Contracts -- sometimes faceup, but often facedown.  After everyone has played six cards, they are revealed.  Hit Men kill other "Person Cards"; District Attorneys nullify Contracts;  and Reporters are used to cancel out opponent's bribes.  After all Person cards are resolved, each Contract goes to whomever has the most bribery on it.  One-third skill, one-third psychology and one-third luck, Corruption is a fun way to see just who really has the best poker face.

Take 6! (6 Nimmt!)
Players:  3 - 10
Type: Card
Essential components:  Deck of 104 cards
Play:  The cards are numbered from 1 to 104.   Four cards are put in the middle of the table, and everyone is dealt 10.  On each turn, everyone simultaneously puts a card face down, and when everyone is ready they are all revealed.  Each card -- going from lowest to highest -- is placed along side the card in the center that has the next lowest value (so if the four cards were 3, 67, 69 and 100, a 45 would go next to the 3 and a 72 would go along side the 69).  As play progresses, this will form rows.  But if you put the sixth card in a row, you take the other five as points -- and you don't want points.  This is one of my favorites, and probably gets more play on Gamenights than anything else I own.
 

Apples to Apples
Players: 4 - 10
Type: Party
Essential components:  Deck of 432 cards (but you can take as few or as many as you'd like)
Play:  We're all tired of AtA now, but for a while this was getting played nearly every week.  One person is the judge, and they play a card with a Characterist (such as "greedy" or "cold").  Everyone else quickly simultaneously plays a card that has a Thing on it, like "Homer Simpson" or "California".  The judge then collects all these facedown Thing cards, reads them off one by one, and chooses which they think is the best fit.  Doesn't sound like much, I know, but it's hilarious, and a sure-fire crowd-pleaser.
 

25 Words or Less
Players:  Two teams
Type: Party / word
Essential components:  275 small cards (but you only need 19 to play a complete game), game board, timer
Play:  Each card has five words on it.  Two people -- one member from each team -- consult the card and then make bid on how few words they think they'll need to get their team to say all five words within one minutes.  As the highest bid is 25, it's a pretty challenging game, but also a fun and gratify intellectual challenge.  And you often get the pleasure of seeing someone pull off the amazing feat of succeeding on a bid of eight or below.  More cerebral than AtA, but every bit as fun in it's own way.