War
War is a simple game that takes nothing more than two players and a deck of cards. Shuffle the deck, and then deal a card to one player, and then to the second. Repeat this until the entire deck has been dealt out. Once both players have their half of the deck you each turn the top card over. The higher card takes both of them and puts them in a separate pile on that player's side. Continue until you've had a separate drawing for each card in the deck. Then re-shuffle the piles each player has and begin again. If you tie (say each player puts out a Jack) then deal three cards face down and turn over a fourth. The highest card on that draw takes all the cards and puts them on their side. Play continues until one side is out of cards.
Go Fish
Go fish can also be played by boys or girls and only requires two people. Shuffle a deck of cards and then deal each player a hand (five or seven cards depending on your preference). Then set the rest of the cards down. The player who didn't deal begins by asking the player who dealt if he has a certain color and number of card. The player asking must have the color and number of the card she's asking for. (The first player may ask if the other player has a red eight, for example). If the other player has that card, he must hand it over and the first player puts the pair face up on the table in front of her. If the questioned player doesn't have that card then the first player draws from the deck and the players reverse their roles. The winner is the player with the most pairs after all of the cards have been paired up.
Block Dominoes
Dominoes are tiles with numbered dots on them that can be used to play a variety of games. In the most basic version, two players shuffle the dominoes face down. Each player draws seven tiles, keeping them hidden. The player with the highest ranking double-ended domino goes first by placing that tile down in the play area, face up. The next player must put a matching end of one of his tiles to the original tile (so a double tile that has two fives could be placed end to end with a tile that has a five and a two). The players go back and forth placing tiles together at matching ends. Players can draw from the boneyard of unclaimed tiles if they don't have a tile they can play, but in some games that isn't allowed and players only have the tiles they began with. If a player can't place a domino then he passes in this version. You win this game by using all of your tiles first.