All you need is...

I made a very important discovery at Camp Currie. Happiness consists in getting enough sleep. Just that, nothing more. All the wealthy, unhappy people you’ve ever met take sleeping pills; Mobile Infantrymen don’t need them. Give a cap trooper a bunk and time to sack out in it and he’s as happy as a worm in an apple—asleep

Starship Troopers, CH 4 - Robert A. Heinlein