Kids meals are your friends, you can even get them at TS if you want. I always eat a kids meal at QS because I just don't eat a lot and even those sometimes are too big for me. Get fruit instead of fries. Water, water and more water. Don't be fooled by the fact that you walk long distances at WDW, yes you will walk miles but most of those are not calorie burning miles. You are not usually walking fast enough to get your heart rate up and you spend a lot of time standing. I actually still do a morning work out every day when I go to WDW, I used to jog around the resort but I blew out my knees so now it's a fast walk and then I follow that up with a little yoga. Counting calories is hard because they aren't listed anywhere but if you have been doing it awhile, you pretty much know your portion sizes and to stay away from sauces and cheeses and fried food. Every restaurant has something healthy on the menu and there are fruit stands in all the parks.