I almost wonder if the schlep through the parking lot, into the amusement park and to the food stand, and back to the car every day offsets the bad diet. And if not, how many steps would do the trick?
You pose an interesting question, but OTOH exercise does not offset a poor diet. No amount of CrossFit is going to save you from a daily diet of gravy fries and chicken-fried double-double burgers.
I think exercise is more important than diet. There are many examples of people who literally only eat one food (often pizza) and doctors pronounce them surprisingly healthy. Athletes that need lots of calories often consume what would seem like a bad diet.