What I would consider the "best" are as follows:
-- large Costco/Superstore muffins in a variety of flavors, cut into quadrants for easier eating. One of those muffins is 700-800 calories so will take the rider quite a ways
-- Potato chips/corn chips/pretzels and salty stuff like that
-- Non-diet fruit drinks or pops, like Coke ... and LOTS of it. Way too many organized rides I've been on have been stingy with the drinks. Keep in mind that riders must drink one 750 ml bottle every 1 to 1.5 hours while they are out there. So if you've got approx. 7-hour century riders, they will need at least 3 litres of fluid each ... and more if it is a hot day.
-- COLD water would be lovely. I've yet to be on an organized event that didn't have water that tasted like it had been sitting in a swamp under a blazing sun for the past week. Bleck.
-- Apples and oranges, cut up into manageable slices.
-- Bananas ... lots of bananas!
-- Dried apricots would be lovely ... they are loaded with potassium and go down very well
-- Salted almonds would be another lovely addition to a century menu. They too are loaded with potassium and go down well. I usually buy a package when I'm out on a long ride.
And IF you feel you MUST provide peanut butter, provide it very separately from everything else. There are lots of people out there who are allergic to it. DO NOT provide it as the main choice. I have been on organized events where I was offered pre-made peanut butter sandwiches, or ... nothing. And I had to do the ride on the energy bars I brought myself. How disappointing.