Get the game "Hive". There's a full-size version and a travel version; both use hexagonal bakelite tiles with no board, so the whole thing fits into a (very) small bag. The game is great, but only works for 2 players. If you want something heavier (gameplay wise, not weight-wise), Race For The Galaxy is very, very good, nearly infinitely replayable, and is only a few decks of cards.