The day after is actually part of the experience, if you ask me. Lolling around with most of the people you rolled with the night before is great fun. Light meals, lots of juices and coffee and water, maybe a few sinful things you wouldn't otherwise choose to eat. That's about all I would advise attempting.
After giving it a day off, then hit the gym (if that's your exercise thing). Me, I just go for a nice long run. But not on Sunday. Like Monday at the earliest.