I don't eat much of anything for 3 to 5 hour rides, maybe a couple of cliff bars or bananas, unless you haven't eaten in 12 hours then you might get into trouble. For 5 to 10 hours or more I eat a regular lunch meal (subway or something that I find along the route). Sometimes it's 2 hours into the ride sometimes more. It depends on what you body can handle. I can't handle to many protein bars anymore I have to have real food. Some can't handle real food and live on boost or heed or something. I would carry what you think you'll need and plan on getting something along the way and try to see what works for you, each person is different.
A general rule around here is 200 calories every hour after the first 2 hours or so, but again, each person is different so find what works for you. For me, that doesn't.