Well i've done this before and its great fun, tips i'd give are as follows.
1. Keep the background music lively but not blaring.
2. Take a half hour break every 4 hours for munchies and general chat, getting characters and room in order etc.
3. When ordering food make sure you do it before they close <chuckle>.time really does fly when your having fun on an all nighter.
4. Make sure everyone is able to get to where they need to be the following day, nothign worse than a player saying "er guys can I get a lift now I'm due at work in 10 mins" when its the first anyones heard of it.
5. Bright light, make sure you keep your room lit, nothing like half light for making people snooze.
6. Plan several lively encounters during the session, that way just when people think things have quietened down they suddenly have to get with it and keep the brain in gear.
7. Make sure there is a toilet nearby a bladder will only hold for so long LOL
8. Keep things moving be sure to keep all players involved in what is going on, make a conscious effort to check what every PC is doing on a regular basis.
9. Using Miniatures is another good way of keeping folks focused on an all nighter as it keeps thier attention focused on whats going on and thereby gives them less time for their minds to wander and to fall asleep.
10. Plenty of Caffeine, keep the coffee pot filled
