Another "lifer" here. After losing my weight about 3 or so years ago, we still do our 3 or so trips to WDW every year, however I may it a point to incorporate some kind of workout almost every morning we're there (I may skip a day or 2) but I either do a 30 minute run or if it's too hot, most of the resorts we stay in have a fitness center and I'll jump on an ellipitical for 30 or so minutes. Then I do a little strength training.
I know you can walk many miles while at Disney but as a previous poster mentioned, it is not cardio. Stop & go walking is not cardio, so a quick cardio session is a good idea if you can swing it somehow.
As far as the eating thing goes, well the best advice is pretty much a little bit of what many of the previous posters mentioned. Small portions are the key, don't feel as though you have to clean your plate. If you end up throwing part of it away, better that than in your stomach! You pay for a meal and whether it's small or big, it's what it is. Try to make smart choices sticking more with fish and chicken with veggies than steak and burgers with fries, etc.
I tend to order appetizers rather than entrees in many cases. I'll even split an entree with my dd or dh and get an appetizer if I'm really hungry. Sauces and dressings on the side whenever possible. Veggies dry, no butter.
I try to eat salad whenever possible and 1 dessert a day, that's it and still try not to go overboard with it. The toughest thing is the buffets. If you have no willpower stay away from the buffets!

I will take a very small amount (tastes) of items from the buffet and place them on my plate and that's usually how I'll eat from a buffet but I only schedule a few for the duration of our trip.
So far I've never returned weighing more than when I left. It's just incorporating what you've learned from WW as far as how to eat and getting in some cardio. Also make sure to log what you eat too.

Good luck and enjoy your trip!
