First off, we always eat a LOT at WDW - usually a lot of buffets. When we were on the go a lot, we might not gain any weight. But when we slowed down for a trip with DD, I came home 9 pounds heavier after 6-7 days. Most of that was water weight though. WDW's food is generally HEAVY on the sodium. So plan on some water retention as long as you drink a healthy amount (which we do). I was probably down to a 2 lb gain after a couple of days, on that 9 lb gain trip.