Some general rules:

1. I try to get through about a bottle of water each 90 minutes of riding.

2. For a ride under two hours, I don't plan on needing to eat any thing. It's really not necessary. For rides of two to four hours, I'll either stop for a quick snack, take an energy bar, or mix up a bottle of Hammer Perpetuem. If I'm doing Perpetuem, then I'm consuming calories pretty much from the start of the ride. For rides longer than 4 hours, I get more careful about nutrition, and really make sure I am consuming enough Perpetuem each hour.

3. I take a break (restroom, refill water bottles, etc.) every 90 minutes or so. Usually these are pretty quick. If I am somewhere scenic I am stopping more frequently just to snap photos.