I did a comparable rid a few weeks ago - 64 miles with around 3,300 feet of climbing. Fairly warm day - hit the mid-80s.
At home, before leaving, I had a bowl of cereal and a grapefruit (kind of my normal breakfast). I think I had a couple of toast before leaving the house. My ride start was a little over an hour drive away. Just before starting to cycle, I had a banana I brought with me. I carried a couple of cliff bars with me along with a few pickle spears (I've gotten kind of attached to having pickles on my longer rides). Brought three water bottles with me. At about the 26 mile mark, having done two of the three long climbs, I was feeling like I didn't have enough to eat and drink to take me through the whole ride so I stopped at a convenience store and bought a banana, a small package of chips ahoy cookies, and a liter of gatorade to replenish my water bottles.
Not sure about the science of what I ate and drank, but I actually felt pretty good after the ride so I was happy
