So I'm going to assume with ********** that this is some sort of benefit ride. People do sometimes get worried about doing these kinds of distances when they have signed up to do the "Tour de Cure" or the "Race against Hipsterism". This is mostly because they have analogized the distance to what might be a comparable running event AKA the marathon.

A century is not like a marathon. Leukybear just finished metric centuries 12 days in a row and I don't think he would claim to be a world champion. If there are ultradistance runners who could run a marathon 12 days in a row they are extremely few in number. The Tour de France involves these kinds of distances for more than two weeks. Bicycles are simply a much more efficient way to travel and they need not involve a great deal of damage to the body, if done for even very long distances.

Basically when it comes down to finishing a century the only thing you have to do is keep pedaling. Following the advice above about hydration and nutrition is good. Don't try to be fast. In these kinds of rides, you are very likely to not be timed at all. They will could have a staggered start and they will have no way to keep track of your time. If you want a time, bring a watch or a cycling computer. In this kind of situation you do not need to worry about being shot out the back, so strategy-wise the best thing to do is find some riders at a pace you are comfortable with and hang with them. Most importantly have fun.