Well, when I was out in the desert, I had plenty of smokes, hot sauce and socks.
Small, portable game sets (Chess, backgammon, etc.) My driver had a small chess set. After 6 months it was pretty much destroyed from use, but we sure as hell enjoyed it.
Books! Fiction, Non-Fiction, it don’t matter. Paperbacks obviously, for size and weight considerations. Get enough people getting enough books in and you start a book swap. Hell, if some of the other troopers get bored enough, you can swap details for books!