Besides stale cookies, what else do they like to get?
When my son was stationed in Sinop, Turkey, I sent him an "instant birthday party kit." I put in one of those "mix and bake in the same pan" cake mixes, a container of CHOCOLATE frosting, a couple of cans of nuts, party hats, noisemakers, and some little party favors. For Christmas, I got a big plush stocking and stuffed it with all kinds of little games, rubber critters, puzzles, small toys, and a pair of Groucho glasses. His buddies just LOVED it when he got packages from his mom, because there was always something in there for everybody else.
Canned butter cookies from Sams will keep and travel well.
Jerky.
Even a stick of summer sausage will probably make it intact.
Microwavable popcorn. (there might be a microwave oven somewhere...)
Hard candies.
Decks of cards.
Cigarettes, if they smoke or have smoking buddies.
Joke books.
Writing paper and ballpoint pens. (pencils need sharpening, so if you send pencils, send a couple of little sharpeners, too)
Paperback westerns, other shoot-em-up books.
Prayerbooks.
Comic books: Spiderman, Batman, etc.
Wooly socks for sleeping in the mountains would probably be welcome, too.
Bandaids.
There are all kinds of things that they would appreciate. Think like you were planning a big backpacking trip for a long time, and that will give you an idea of what will make the trip and be useful.