1000 blank white cards
1000 blank white cards is a card game without any predefined rules. Most of the game can be tailored, before the game, or even during the game!
You need lots of empty sheets of paper, roughly in the size of playing cards.
The game is usually played in a fashion similar to collecting card games like Pokemon or Yu-Gi-Oh. The players compete each other with their cards. The winner of a duel wins against the competing player.
The interesting aspect of this game is: there are no predefined rules. The rules are made up during the game by the players. You can define your own cards during the game. Of course, some rules can limit, what kinds of cards you are allowed to create (or use). Remember: those rules, too, are created during the game, and can be modified as well!