My son was in Iraq (Marines--ooh rah) with an FOB and was most appreciative of handwritten letters (until he got to email)
his camera (he got some great pics!)
everyday snacks (doritos, etc)
BUT HIS ABLSOLUTE favorite were the care packages that had cans of his favorite soda, MT DEW! If you pack them right, they will travel well. He was very popular when those arrived!