After being over there for awhile everything you brought with you starts to break about for about month 4. (Or sooner) So just ask him. When I was there we had nothing cause it was the invasion.
But Headphones and or portable cd players are all you have to get your mind out of the sandbox. So music was a big thing. If he is into music pretty much any cd that isnt top of the charts you cant get over there.
A portable dvd player for when you are in your tent at night is the best thing ever but like I said sand and dust eat stuff quick so he might have one now that is his lifesaver (mindsaver) in the evening but that doesnt mean it will be working in about a week from now.
Cool things that he can show off the guys that you would want to get him are:
Check local laws to make sure Auto opening knives are legal where you live so you can order them He can have one cause he is in the military. The first one is the knife that Special Forces get issued so it will be the envy of all, this knife actually has an NSN (National Stock Number) So that means that Military or Federal employees can order it and it is approved. But of course civilians can have them too. There are non Auto Versions of the the first knife.
The second knife was shown to me by a guy in Delta Force way before I saw it in any mag or store. Benchmade for the most part has the lock on the SF guys, they love their knives. But anyway this knife is pricey but is the baddest knife next to MicroTech knives. But half the price. Which isnt saying much cause it is about $500. Benchmade also make a push dagger that alot of guys like over there.
http://www.benchmade.com/products/product_detail.aspx?model=5000http://www.benchmade.com/products/product_detail.aspx?model=3300Also if he doesnt have one and you are looking to get him something not involving knives or such, is a good watch. There are a ton out there that are good of course. Really I love just the Timex Expeditions with the velcro strap. I never liked the feeling of a rubber watch band with sweat and sand on my wrist. And if you wanted to to go all out on a watch. 5.11 makes some cool ones and the company Special Ops Watch makes great ones.
Any little thing helps too. Good Socks, Kool-Aid, Suckers (Blo-Pops) If you can find them the Under Armor undershirts are nice, Better than plain Cotton. And of course Good Gloves. Mechanix Gloves were my Fav. But he might like Hatch, Surefire, or Blackhawk Plain aviators.
I hope some of this will lead you a direction. Everyone added good stuff. Make sure that he knows that there are alot of people that still care and will always.