Jessica, you'd better investigate gels or bars or something- crackers arent going to keep you going. At a "real" Century, hopefully, if well-organized, they will have SAG stops every 20 miles or so, with fruit, sandwiches, candy, pretzels, everything you could want. Eat whatever your body tells you, in a comfortable amount. Or maybe a teeny bit more than comfortable. I definitely wouldn't say a "big" lunch.

Nanci