Before you go to bed after a night of partying, drink a couple glasses of water or gatorade. If you wake up in the middle of the night, drink some more, and then again when you wake up in the morning (or afternoon). If you don't have gatorade or other sports drink, take a multi-vitamin that contains potassium and Vitamin B. Bananas are great sources of potassium, and would make an excellent addition to your hangover breakfast.