There are many commercially available items that can be used as on-bike food. For instance, you can use Clif Bars, cut in pieces for easier handling. The snag is that the pieces tend to stick together. If you get tired of "boughten" food, are riding where stores are off the route, or just don't care for what the stores offer, Feed Zone Portables is packed with recipes for take-along snacks.
Rice cakes, for example. I first saw these mentioned in The Cyclists's Training Bible, and was puzzled. The only rice cakes I knew at the time were the kind you buy in the grocery store, and which don't stay crisp for long after you open the package if you live in a humid climate.
Once I began reading the Feed Zone books, the mystery was solved. These rice cakes are made with sticky rice, e.g. sushi rice. Now that I've made them several times, I see that the possibilities are all but endless.
You can cook red lentils with the rice, if you like. Add onion and garlic as you like. Or cook the rice, then add chocolate bits, stirring to mix them in. The advantage to making my own on-bike snacks is that I can put in exactly what I want!
Some of The Feed Zone Cookbook's non-portable recipes are becoming favorites with me. Simple Biryani (p. 224), for one. I keep in mind, however, that a number of these dishes are high in fat. They were developed with pro cyclists in mind. Those athletes train hard for as much as 30 hours a week, and I guess they burn off the fat, and certainly the calories.
Therefore I look for recipes with a lower fat content, and/or try to reduce the amount of fat. Take the aforementioned Simple Biryani. The recipe uses 2 Tbsp. of light olive oil. I have only the regular kind, so I use half the amount. And before I start cooking the veggies for the biryani, I put on a small saucepan of water to heat. When the stuff in the pan seems to be getting too sticky, I sprinkle in a teaspoon or two of the heated water. It seems to work fine.
So don't be afraid to experiment. Just start slow and easy if cooking is new to you. And now, if you'll excuse me, I'm making myself hungry. I think I'll go eat a rice cake or two.