From everything I have heard, you need to eat on the century what you have been eating while training.
You have been doing long rides before now, right?
What have you been doing on those rides?
I am workimg up to my first century myself, still haven't tried any solid foods, but I drink Accelerade and use those Gu shots, about 300 cals an hour for rides over two hours. Next step is to see what solid foods I can eat while riding.