Doughnuts. Nothing better for cheap, fast energy. I discovered this (and I hated doughnuts previously) while on a less-than-optimally funded tour, and needed something to fill the energy void. I have a high metabolism, and realized that I could eat as much as I wanted every day and still lose weight, while burning up to 4000 calories a day. Doughnuts filled the calorie hole nicely, with the delightful combo of fat/sugar/starch.
The best doughnuts in the world are in a small bakery in Cardiff-By-The-Sea, California (between LA and San Diego). If your doing the West Coast route, I absolutely recommend you stop in on them. Just ask anyone in town...