We've been on qsdp and haven't spent any extra money in parks. With the desserts we choose something we can snack on later and don't eat them at the meal. And even doing that we still had too much food. Now we stop and buy a case of water too at the store for the week before we get to the resort.
We have also done budget trips a few years back where we do no dining plan and pack lunches in the parks and eat in our villa at night with the exception of one or two times. The kids have been yearly and twice yearly when they were babies up to preschoolers that they didn't need more souvenirs on those trips. Now I certainly like to eat out, but if it was between not going or saving on meals so we could still go at that time, it was well worth the packing of lunches.