I'm one of those, perhaps odd, people who have no problem eating a fair bit before a ride.

Sometimes after I get home from work, I'll readily eat a good 400-600 calories immediately prior to heading out for a ride. It isn't really a factor. On rare instances, I may feel I've eaten too much and then my HR gets a bit higher, but it goes away fairly quickly. Riding without eating enough is definitely a problem for me.

While on the bike for a long ride, I try very hard to anticipate hunger. The moment I even ponder for a second, 'am I hungry?', you know, that time where you aren't sure.....I'll just eat. Usually I take energy bars a la, Luna, Cliff, etc. I just haven't gotten into gels and such, for some people they work great I'm sure.

So the night before a very long ride, I just try to eat a good bit. Lots of carbohydrates and another thing, lots of liquids....even if it means I have to get up at 3 am to pee. Breakfast before, is more of the same, and it usually nets me a good 3 hours before I have to eat anything.

Don't worry too much, just decide what you want to do and keep a record - then if it doesnt work out, you'll know for the future.

Good luck with your century.