Most of my gear is depressingly new. I'm going to offer: a deck of playing cards.

Survival has a psychological component, moral matters and boredom is an issue. A deck of cards provides endless entertainment. With a single deck you can play a wide variety of different games, from simple ones like Snap for children, to sophisticated games for adults like Bridge. You can keep score, if you want, or gamble (with tokens or money as you fancy). There are games for groups, or pairs, and many versions of solitaire. The deck takes a trivial amount of space and does not require batteries, and it only costs a few dollars.