Here's another one, but I haven't done it at a retreat yet (the problem at our retreat is that by the time we meet for games, it's a bit darker in the room)
Spoons is a great game for groups. At least three players are needed to play, and more players means more fun.
Players sit in a circle on the floor or around a table. Spoons are placed in the middle, one fewer spoon than players. Each player, including the dealer, gets four cards. The dealer takes one card from the deck. If it improves his hand, he adds it, discarding another card, which he slides to the player on his left. If not, he passes the card on. The player on his left does the same until all players are passing cards.
The first player to collect four of a kind quietly takes a spoon. When the others see the spoon taken, they grab for a spoon. One player will be left without a spoon and is eliminated from play. Play continues until one player is left.