Yes. Both caffeine and nicotine are not something one wants to be going without "cold turkey" in an already stressful situation.

Having inadvertently tried it once, I can tell you the headaches are bad, and I was ready to kill every living organism in sight.

Also, it can serve as a morale boost. I remember my first care package during Desert Storm. It was a simple box of Tic-Tac candy. I know it is simple, but that little box of candies addressed to "Any Soldier 101st Airborne Division" helped to the point I rationed them out for days.