First of all, if they by a desert they are going to be plenty thirsty.
Second, the markup for food is probably at least equal with the markup for those precious souvenirs. And third, since food is a necessity and absolutely nothing else on the property is, then shouldn't they be upset about those other things before the need for sustenance?
Sorry, I hate to bust another myth, but, back in the "golden days" of Disney that everyone seem to remember with exacting clarity, I'm afraid that people that brought in sandwiches, etc. were far more plentiful then the percentage of those that do now. Theme parks were relatively new and anyone that ever went to a Carnival or Amusement Park knew how high priced food was in those venue's. Back in the 70's and 80's when admission was seemingly so cheap, it allowed more people to enact a strict budget and therefore bringing in lunch was the normal way of affording a Disney trip.
I had some friends that made their first visit to WDW in the mid 80's. They brought in PB&J sandwiches. In a resent conversation that I had with their Daughter, now almost 40, she still shivers at the pain of sitting on a bench eating a sandwich when all that gooey stuff was being sold at the counter service places. It caused her to be totally embarrassed. I would guess that she was around 8 or 9 at the time. She always wanted to go with us because we didn't bring food in. It was, however, something that you would see all the time. Some didn't know that you could bring it in so they would go out to the parking lot at lunch time and have a tailgate lunch. I always was concerned about the fact that their car sat out in that hot Florida sun. I hope they owned a very well insulated cooler.
