What can I say to comfort my fiancee who is deploying to Afghanistan?

He's a Navy Corpsman about to deploy with a Marine Unit. At first he was excited, but the closer we get to the day, the more I can see the signs of stress in him. I'm still in school so we're long distance and normally we spend our free time talking to each other, but lately it seems like he'd rather go out with his friends and drink. I guess he feels that he needs it as a release for all of the stress he's under? It's such a touchy subject to approach, but I know he's worried about death...I want to be able to offer him the best support possible. Any advice you have (about what to say, what not to say, what to do) is welcome and very much appreciated!