Hydration is key, but the two days before the ride is as important as the ride itself. If you're not getting up twice a night to pee, then you're not drinking enough. The day of the ride, drink enough to stay hydrated but not so much that you have to visit the giggly weeds at every stop. And I'll put a plug in here for Accelerade... awesome stuff. I did my first sub-5 century last year (actually, my first century ever) and my one stop almost pushed me over 5 hours. I crossed the line at 4:55 and if it wasn't a chip-timed ride, none of my friends would have believed me!