I like the idea of simple games. Playing cards are great. it might be good to think of some game that you can play with things you can make. One could make a chess, backgammon or checkers board and pieces. Adding some dice next to the playing cards may open a lot of options.

I think one should also think about some physical activities. Blast's thing on 100 pushups is great. If you teamed it up with a few more exercises, pullups, dips, situps, burpees, etc., you'd have a routine most could follow and keep themselves in shape, while using not much space or equipment. The more different exercises you know, the more you could vary the routine and avoid boredom.