I've always tried to pack in 3500 calories (~1.5 lbs) of food per day, and I can never seem to eat nearly that much. I'm usually working so hard that having a brick in the stomach isn't desirable and my hunger just isn't there. As such, I typically try to pack food high in fat since it contains 9 calories per gram, versus the 4 calories per gram in protein and carbs. Twinkies, candy bars, Combos, and nuts are not off-limits when you're burning more calories than you take in! I also force myself to eat every 3 hours at most, and no less than 400-500 calories. I've read a couple books of people backpacking the PCT or Appalachian trail, and they are always taking in tons of candy bars. I agree with a lot of the other posts above too.