One of the biggest benefits of the parks is the amount of walking you have to do.
Embrace it (with comfortable shoes, of course).
Want to park hop between Epcot and the Studios? Don't get on the boat or the Magical Motorcoach. WALK!!! (If you take a shortcut through the Boardwalk pool area it's 23 minutes).
And I try to make it down to the gym for resistance training (I'm guessing those on the treadmills don't do the parks).
Part of the joy is eating in the nice restaurants (mostly in the resorts and not the parks unfortunately). So I try to save the calories for the good stuff. At Boma I eat like a bird (I'll literally put one bites worth of each thing that looks good on the plate - which results in 4-5 trips with half empty plates - then one trip with seconds). I don't worry about 'cleaning my plate' (it's used as feed for animals what you don't eat). Breakfast is OJ, chocolate milk & donuts.
When practical, the 'big meal' is best for lunch rather than dinner. Marrakesh is *far superior* for lunch (better ambience and much better to enjoy the entertainment).
Some 'sig' dinners can be had relatively early in the evening. (Cali grill is good [provided that it's still good after the redo] for a marathon MK Saturday (eat at 5:30, then burn it off until the late park close). Epcot resorts are convenient to Epcots 9pm close (provided you finish and make it to the gate before it closes). Unfortunately, some others end up being not only late, but the very last thing you do, so it doesn't burn off that day.
And once in a while, embrace your hunger (providing you don't have low blood sugar). You don't have to finish those 'Cockerell Fries' if you got a soggy batch. Don't get extra onion rings with the rib plate at AK (unless you have a large family and can split them). If at a meal and what's in front of you is merely passable, eat just enough to eliminate discomfort. (Unfortunately some locations are basically 'feed stations'. If you must eat there, eat as little as possible).
If at F&W, if you try something and you don't like it, don't finish it.
If you don't enjoy alcohol, don't have it just because everyone else is. It's not only high in calories, but it slows your ability to burn those calories. And if you do, for the sake of everyone else, moderation please...
As much as you want to enjoy the good food that they still do have, you also want to look good when you get back. You want to be noticed for the tan you got not the tire you added
