Over at The Teaching Nest, Lauren posted a great game that requires kids to strategize how to take 1 to 2 Unifix cubes away at a time (from a stack of 10) in order to avoid being the person stuck with the last cube...the "poison" cube.
My kids play a similar game, often while riding on long car trips. It's also a great classroom game. Here's how it goes:
Players: 2 or more
Object: Go around the group, counting to 20 by saying either one or two numbers. Avoid being the one to say "20" as 20 is the "poison" number.
So a group of 3 kids might say:
Bob: I'm stuck with 20!
The more you play, the better you get at strategizing how to avoid 20.