Eat your body weight in grams of carbs about 2 hours before ride start. For example, I’m about 150 pounds, so I eat 150gr carbs for breakfast. I also do this for workouts over 2 hours and hard group rides. I eat 90gr carbs per hour if the ride is hard. Otherwise, I just top off carbs before an effort is coming up and eat minimal food if I’m sticking to endurance zones.
Most important for me is staying on top of water and salt. If I do well on that, no cramps. If not, I will cramp. For that reason, I drink a ton of water all day and night for a couple days before, and I try to eat salty food.
I did a 4hr 41min elapsed century (including two stops to get water) about a month ago, and this worked well for me.
Another thing, what doesn’t work for me is eating solid food towards end of the ride, as that makes me nauseous. Been there and those last miles can be hell when you want to puke!
Everyone is different so you have to practice nutrition to find what works. Ideally, I know I’ve done well when I still feel pretty good at the end.