I just got back from afghanistan (army infantry), Go for an ESEE knife, the 4 or 6. There isnt much chance hes going to need to fight with it, Theres alot of chance hes goiung to have to use it as a tool. Hell probably be living in a little fob made of hescos and hell have to make whatever he needs, so he needs a good solid utility knife that can work as a fighting knife, not a fighting knife that can barely do utility work.
The ESEE-6 has plenty of blade and a flat grind that will allow him to easily perform anything he needs to do, and at 3/16 inch thick of simple 1095 hes not going to have to worry about breaking it. The sheath is solid and will blend in With MARPAT if you go with tan just fine, its a great knife at a reasonable price.
Ive always had honorable dealings with derrick at KSF :
http://www.knivesshipfree.com/ESEE-Knives-ESEE-6p-Knife-wLinen-Micarta-Handle-1095-Steel-ESEE-6p
another word to the wise and gift idea for a guy going into a hot zone ENO hammock with bug net:
http://wwww.eaglesnestoutfittersinc.com/pronest.html
http://wwww.eaglesnestoutfittersinc.com/guardian-bug-net.html
Those things are worth their weight in gold, Hescoes which your son will in all probability be living in shift and move with rain, because they are filled with dirt and they turn to mud, everything on the ground gets soaked in mud, and if you are asleep on the ground or on a cot you cna sink a little in and then be covered in mud, wet and miserable with no real way to get clean except for baby wipes.
Another problem with living on the ground is there is a host of snakes and insects that your son will be cohabitating with, we had a guy almost get killed by a damn snake in the middle of the night, he survived numerous firefights almost gets offed by a freaking snake, that would have been a true tradgedy. another big problem is malaria, When your son deploys hell probably start taking doxycyclin :
http://en.wikipedia.org/wiki/Doxycyclin
The thing is that doxycyclin isnt all that effective the military makes you take it because it has some effect but theres no garantee that it will protect your son,
ENO hammocks are great because they are light and packable each end had a D-ring/carabiner that you can hook into the wire on the outside of hescos or onto something else with 550 chord and you cna suspend yourself inside the hesco barrier and be off the floor.
They pack down small and even if hes packing light and not using a full ruck he can just strap it to the outside of the pack and go with it adding the the misquito net just keeps all those damn biting insects away which is in and of itself a small miracle.
Im, just telling you this because small comforts mean alot to a guy in the feild.
Good luck to your son and tell him to keep his head down.