Eating and nutrition takes personal experience as different people have different needs and reactions. I know people who don't eat anything on 100 mile+ rides using liquid based stuff (like Perpetum) instead. On my long rides, I like PB&J sandwiches. I typically eat 1/2 sandwich for every 30 miles or so I ride, plus a Gu for the featured climb of the ride.
Your training rides will not only help you get in shape, but help you learn what foods work for you and which one's dont.
For instance, I learned that high fiber food the day before a long ride is a bad bad bad idea for me.
