Last year I was doing some 4-5 hour gravel rides. I started bringing along a couple peanut butter sandwiches plus a couple bars. The peanut butter with some fat and protein seemed to do the job of providing good all day energy. I’ve also used those Justin’s peanut butter packets on rides.
Anecdotally, I’ve heard an interview with a former RAAM racer and he said the secret food was olive oil.