I rode 35 miles last evening with two Cliff bars in my pocket. Came home and set them aside for the next ride. On a 50 mile ride I might eat them. 70 miles, them and a PB sandwich. But I often come home with uneaten food.
In my racing days I rode my 45 mile loop early before I ate anything. Did it in 2 hours flat once, honoring traffic signals. For important races, I ate nothing but fruit and liquids the 24 hours before.
Now conditioning counts for a lot! I've ridden 70 miles on nothing but Vitalyte in my water bottles. I've also ridden 40 miles when I wasn't in great form and had to eat my way through it.