I've done 100 mile rides but never an organized century with pit stops, but that sounds like a lot of food.
Night before: good, well balanced dinner.
Morning of: big bowl of oatmeal, fruit, coffee.
Ride: take some bananas/cookies/bars/whatever will fit in a jersey pocket
Mid-ride stop at gas station/convenience store: soda, candy bar.
I mostly go by feel, and the main thing for me is to make sure I'm taking in enough fluids.
For 100km, I'm probably not stopping in the middle, so a Clif bar or banana or a ziploc bag of cookies is fine.