If you're planning on putting this build in a desert (or any hot weather) environment, you'll need water...lot's of water! Typically, troops will carry at least one day and sometimes up to three days worth of bottled water with them. Two or three cases and some individual plastic water bottles will serve this need nicely.
The only other thing I can think of is maybe a couple of extra ammo boxes of M-16 ammo sitting out.
Edited: Oh, how about a box or two of MRE's?
Looking good,
Robert