Are you talking chemical enhancement or methodology?
Chemical wise, GHRP's and GH are both known to stimulate appetite pretty heavily. I eat like crazy after pinning GHRP-2 + CJC w/o DAC. There's also insulin which helps me move crazy amounts of food pretty easily.
For methodology, i think keeping up appetite can be accomplished a number of ways. Cardio 3x a week for 30 minutes helps a lot to stimulate hunger. On top of that, I make sure to choose foods that work with my body. Through trial and error, I learned that wheat doesn't do well with me and neither do oats. I stick to white rice (brown rice bloats me) and potatoes (sweet and white).
For meats, I don't eat too much red meat as i feel the fats really kill digestion. Lots of chicken, turkey, rarely pork and a lot of fish (swai + salmon). I also don't consume much dairy as I've noticed it bloats me pretty bad and disturbs my digestion. Also, vegetables (romaine, spinach, asparagus, etc) have been really important in helping move digestion along so I don't get backed up.