Haha, I would probably collapse of fatigue if I only get 4 hours of sleep a day. But seriously, I never drink pop before I go to sleep. Drinking tea is not such a good idea either since tea contains caffeine, unless you drink the ones with decaf. And yes, caffeine makes you stay up =P.
A nice cup of milk puts me to sleep nicely ^^. I find my body more relaxed when I listen to my mp3 to make myself more calm, but unfortunately, I don't want to waste my battery.