A few things from past experience...
share meals with anyone who will share with you.... (you can always go back to order more if you are still hungry, but if you are full and the food is still in front of you, you will probably feel compelled to finish it.)
salads (bring your own dressing in packets if desired)...
hot vegetables (available anywhere they sell complete meals, such as at Cosmic Ray's in Fantasyland, and Flame Tree BBQ at AK)...
fruit (plenty available if you just look)...
veggie burgers (just watch the toppings and portion size)...
grilled chicken (again, watch the toppings and portion size)...
make up your own meals by ordering things al a carte....(there is no Disney "rule" that you have to get fries with EVERYTHING!!)
Avoid burgers, pizza, fries, ribs, hot dogs, "salads" such as tuna salad, chicken salad, and cheese. None of these things is so "special" or "wonderful" at Disney as compared to other places and they are LOADED with fat and sodium.
Order everything "on the side" so you can control the portions of condiments.
If you are truly hungry and craving something that you probably shouldn't have, take the following steps first....
drink a large cup/bottle of water.... sometimes dehydration can mask itself as hunger.
have a smaller healthy snack, such as fruit.
If you still feel truly hungry and still want that _____________________ (fill in the blank with your favorite Disney treat), have it! Better yet, share it with a loved one! My kids will often let me eat an ear off their Mickey ice cream bar. It is more than enough of a treat for me usually.
Try to stick to one special dessert per day... usually at a sit-down place if you have reservations. If you have that to look forward to, it is easier to pass up everything else that comes your way.
Hope some of this helps (and hope I can take my own advise next week!!
).............P