All good advice here. If it is a supported ride, and most Charity rides are, more than likely you will get plenty of food. They will have sag stops about every 20 miles normally. The route sheet will tell you how many and how far. Pace yourself and as it was said drink before you are thirsty and eat before you are hungry. Don't skip a SAG stop just because you are feeling good, you can judge that after your second century. Whenever you get the chance get in with a group that happens to be going about the same pace as you. If you can't stay with them don't worry about it but while you can it will be easier.
Most of all have fun, look around and realize you are doing something you enjoy and not working.