What does he do in the Army?
A lot of folks think a Multi-tool is more useful than a large fixed blade.
There is the Leatherman Xt, which is one of the better available. Titanium frames and a 154CM (Better than the ususl blade steel you find on Multi-tools and a lof of knives) It has scissors which may be a lot more useful than you think.
The Cold Steel SRK (about $50-60) is well thought of and if lost or stolen won't make you weep. Other reccomended knives are BK7 BK10 RAT's Rangers Swamp Rats)
If I were buying for my son (and I know you want to get him the best, because, hell, its your son) I would still not get a $300.00 fixed blade. Not because its 'too expensive' but because it wouldnt get as much use as you think it would.
For $300.00 more or less I would get
my son
Either a SRK (Image taken from sightm1911.com)
A BK7(Image taken from Lippman-enterprises.com)
A Leatherman Charge Xt (Image taken from all-leatherman-tools-4-less.com)
A decent Flashlight like a Surefire
www.surefire.com or an Inova
www.inovalight.com or a Pelican M6 LED
Get him one that has a removable red filter on it so that he can use it at night and not damage night vision.
Then a handy and light sharpening stone or system DMT are probably the lightest.
I'm sure lots of guys here will chime in.
Wish him the best from us here. :thumbup: