Tic-tac-toe is an absolute timeless game that you can whip out no matter where you are and know you'll have some good friendly competition. You can play with some pencils and paper, you can buy sets, you can play with chalk, and you can even make game pieces with rocks. As long as you have some game pieces that are two different objects, you're good to tic-tac-toe.
If you or someone you know crochets, then you can make one that's perfect for traveling with so you have it whenever a game calls!