Yeah, anything really, as long as it won't spoil in transit or as soon as he opens it - jerky is better than chocolate. Couple of good toothbrushes would go down well as everything gets covered in sand, if he has a laptop with him, download the latest movies and send them out on a memory stick.
I got my folks to send me out all sorts of shit when I was out in Bosnia, mostly chocolate though. When my buddies went out to the sandbox in '03 I sent them traditional Scottish stuff - haggis, neeps & tatties (tinned & dehydrated) they loved it!
The US ration packs are a damn site better than the shit we had to put up with so you won't have to send out too much in the way of edible comforts.
Tell him we're all rooting for him too!