I recently went on a ride that was supposed to be 45 miles, but I couldn't get past 35 before practically falling over on the bike. The reason? I didn't bring any water OR food to keep me energized. Dumb move and I hope it never happens again!
Lol but anywho, possible examples of good energy food include bars, gels (not as a consistent energy supply though), any food high in carbs, and most types of fruit. The key is to go through about one energy bar an hour, and one bottle of water per hour. This way you'll have a consistent supply of energy and you won't bonk in the middle of a ride.