Nim
is such an easy math game to set up and play because you can use almost anything and it only takes minutes to play. You use an agreed upon set of objects. If you are outside, you can play with sticks or small stones. If you are home, you can use any objects you have collected around the house. Today we used toothpicks. 
We decided to use 10 to start with. (Incidently, it took ten toothpicks to spell the word NIM at the top of this post.) For each turn, each person is allowed to pick up either 1 or 2 objects from the pile. The person who picks up the last object, even if it is part of two, wins. You can modify the game to have more objects or allow a different amounts for pick-up. You could also have the last person to pick-up loses instead of wins. The origins of this game are unknown, but a game similar to this was played in ancient China, and so many attribute China to it's origins.
We decided to use 10 to start with. (Incidently, it took ten toothpicks to spell the word NIM at the top of this post.) For each turn, each person is allowed to pick up either 1 or 2 objects from the pile. The person who picks up the last object, even if it is part of two, wins. You can modify the game to have more objects or allow a different amounts for pick-up. You could also have the last person to pick-up loses instead of wins. The origins of this game are unknown, but a game similar to this was played in ancient China, and so many attribute China to it's origins.
Also, if you turn the word NIM, like as written in toothpicks at the top of this post, 180 degrees, it spells WIN.
