I always intend to exercise while we visit, it just doesn't happen. I agree, walking the parks 12 plus hours a day is enough most of the time. I DO watch what I eat. I eat mostly salads as there are a lot of good options. I will indulge in a Mickey bar or something else yummy. But, I don't go hog wild. I gained 5 pounds last year and lost 3 of it when we were home after the second day.
Have a great time!