I like to keep a Clif Bar handy (chocolate chip is my favorite). Clif Bloks, as another mentioned, are pretty good, too. If you don't like riding with a feeling like something is on your stomach (which is the case for me sometimes), I also use Gu gels for energy. Just eat one about every 30 - 45 minutes and drink at least 8 oz. of water. Works pretty well.