Be careful of what you put in this box. He'll likely not have a lot of space, and will have to pack it up and put it into his rucksack/duffel bags. Framed photos are great, but where and how will he pack them? If he has to hand carry them in his carry-on, are they heavy? Will glass break? Is the artwork in a sturdy folder?
Basically, just think of what he'd have at home during his day that he might not have ready access to there. Put little bits of home in that box.
I advise that you put the photos onto his laptop. He can set it so that the screensaver is a slideshow of all the photos. You can put them on a thumb-drive and put it into the box. You can even scan in copies of the kids' artwork and put those into the slideshow as well. Then there's no worry about ruining anything, or having to pack a breakable item.
If he doesn't already have an MP3 player (like an ipod or Zune), get him one and put all of his music on it. A several audiobooks too. If he does have one, get him a set of Bose earbuds. They drown out the noise of all the morons around you on the plane and in the barracks, are comfy, and the sound is AWESOME. They're about $80, but completely worth it to a deployed Soldier.
Is he a coffee drinker? REAL coffee is a godsend. Put in a nice, small-sized thermos and some of those new Starbucks Ready Brew packets. We usually have easy access to hot water or crappy coffee...he can use hot water to make good coffee. A few Splenda packets and a small container of creamer if he uses them, too. http://www.amazon.com/Starbucks-VIATM-Ready-Colombia-Coff...
I can think of a lot more, but those should get you started!