Our 2nd anniversary is at the end of May. He's really into sports and his dream is to see every ballpark in the country. So, last year we went to Kansas City for a Royals game, and this year we're going to St. Louis to see the Cardinals. (I figure I can ride this theme for a while and not have to think up something new every year!)
I love the dog tag idea! You should definitely do that!! He'll probably roll his eyes now, but when he's over there they'll be really meaningful to him.
I know from a friend of mine who just came back from Iraq that things get pretty boring over there when they're off duty. There's, literally, NOTHING to do. I think you should get him a Gameboy or something like that. Don't worry...his CO will make sure he has no distractions while he's on duty (and maybe he'll play it so much he'll be "played out" by the time he gets back