Depends on what you were using while partying. I always think it's best to eat something before you go to bed (preferably a carb), and drink a load of water so you don't wake up dehydrated. Once you're up again, eat a balanced breakfast (or the appropriate meal for the time you manage to wake). Fruit is a must (bananas tend to be my favorite post-crunk fruit), and balance your proteins and carbs. I love sushi after a night of drinking. If you're feeling in a rut the next day mentally, 5-HTP is nice to help you replace your seratonin levels so you're not all gloom.