There's a commonly held belief that the body can't easily digest more than 250-300 calories/hr if you're exercising heavily. That's about what I tend to eat during long-distance riding. Like Machka, I tend to nibble while touring. My snack of choice is peanut M&M's. They're available everywhere and at 250/cal per package they're pretty easy to ration (1 hr = 1 package). I tend to eat a light lunch, a reasonable dinner, and almost always lose some weight while touring.