Congratulations on deciding to manage your weight! It's not easy at WDW, but certainly doable.
First off, understand that if you're visiting the parks, you're likely to greatly increase your level of excercise, just by walking around. I averaged 20,000 steps per day - or nine miles.
There is fruit available at stands in each of the parks. This is always a healthier alternative to the tempting food in the restaurants.
Drink lots and lots of water! This will also help take the edge off of your appetite.
Don't beat yourself up if you indulge some while on vacation! A WDW vacation can be very, very active, so.... if you take in a few more calories than you expected, it won't be the end of the world. Remember, 3500 calories eaquals one pound, and that's a lot of food to eat. If you make some reasonalbe choices with more fruits and veggies, you should be OK.
Stay away from french fries and other deep-fried foods as much as possible. I've found that the buffets always have some healthier items that I can eat first to fill my hunger, while indulging a little into some of the other items that I just would like to try.
There's lots of chicken and fish options available everywhere...less red meat/less calories.
Good Luck!...and have fun!
- from one whose lost 110 in 18mo, while visiting four times.