Do whatever works for you, but I'd rather have the energy to have a good ride. I can always tell if I didn't eat enough the day prior. That being said, I see a lot of cyclists (and runners) eating way more than they need to on a ride/run. I can do a hard/fast century on a good breakfast (usually 300cal of oatmeal) and around 800cal during the ride, that's providing I wasn't already depleted from the day prior.