I am an athlete, but not an extremely fit one. I do cycling, 5-10 hours a week.

On a good weather day, I can leave the house on the bicycle, ride for 2-3 hours at a casual/slightly-brisk pace, and burn as much as 1500 calories in a day. I bring a light snack & a bottle of water, but i don't go crazy with "nutrition" - just a granola bar & water.

Not putting down crazy numbers either, averaging maybe 80 watts / hour for 2-3 hours. I do this once or twice a month.