I ate this the morning of my first marathon, though I have been eating these long before I started racing (for meal replacements). High in protein, they are satisfying with water. I'm not sure if the carb-dense things are good for running. They top out at about 250 calories for the small piece, so they probably won't upset digestion if you're trying to fuel up. My favorite flavor is below.
They also come in (of the ones I've tried, favorites first):