Though I have no experience with military service whatsoever, I've hiked ever since I was little, and I can imagine that he'd want Icy Hot patches and cream along with hydrogen peroxide, gauze, disinfecting wipes, cotton balls, foot deodorant, Advil, thermal underwear (boxers, shirts, leggings), supportive braces, and any piece of gear that will fit him better than the stuff he has. Focus on things that will keep him comfortable before, during, and after his long walks in the desert. Even the little things can get to you after a while, so tell him that there's nothing too small to fix. Also consider getting him a red head-mounted flashlight, it will allow him to read while he walks without harming his night vision or revealing his position.
-Penguin