We often go and spend nothing. We breakfast before we go, and take our own snacks and drinks. Back to the motorhome for lunch and some cooling off time, and then have fun at FW until dinnertime. Cook a good dinner and then head back for the evening. We usually do our souvenir shopping at the end of the trip and only occasionally buy food in the parks.
This is pretty high. But what I have found works best for my family (wife and kids 22, 21, 18, 17) is to give each of the kids $450 to last them the whole week. They can decide where to eat, what to eat, what souveniers to buy, ect. And the money they have left over to take home is theirs to spend as they see fit. This works well for us, for several reasons. They decide whether they want Lobster or hamburgers; a T-shirt or something more expensive, ect. I no longer have to be the referee, balancing the money between the kids. No favoritism. It teaches them to budget their resources, and to determine the 'value' of what they want. I can relax, and enjoy the trip; and isn't that the entire purpose of a vacation?