I am currently deployed to Iraq, and we get free gatorade at the chow hall. I suggest you send him certain snacks that he likes, trailmix, cookies, gummy bears, etc. Now if there is a certain drink mix he likes that he can not get downrange, then by all means send those. I have my wife send me packages of Arizona Green Tea.
Also, I don't think you would want to send him alcohol, as it's violation of General Order number 1. I have been here 3 times since 2007, and my wife said on this trip, she has been required to show all contents in the box to the Post Master before it was sealed. The same requirement is in place when I send a package home as well. Got to make sure we don't send home "war trophies".