Like Redleg said combat support, but I think there are other ways. Even people in Vietnam who were in combat "jobs" were able to get through the war without firing their weapon, same with WWII. I guess it's just the luck of the draw.
You have to think - it goes from the chemical engineers to the people who keep our ships running, the crews that keep our fighter jets in the air. Communications - some MOSs, they never leave a hub, but they still play a important role in our military or any.
I suppose you could actually include the "paper pushers" and the news reporters, chaplain assistants. It's various.