There are many restrictions about what you can send and in many cases; you need to ask what the soldiers actually want. A few no-no's first:
No Pork. No Alcohol in any form. No Pornography. No Magazines that depict the human body (male or female) in an undressed state (IE: Swimsuit issues, body building magazines, Victoria's Secret). No weapons of any sort.
From the following:
Well, there’s certainly plenty of pork around here.