I didn't had problem with the Fontana village store. I didn't think the prices were too bad and the selection good enough to get me through the park. But SOBO you'd have to stock up at Hot Springs (at the Dollar General) or at Standing Bear, both poor options. Gatlinburg is also a poor resupply, getting to the supermarket is a 2 hour trolley ride - one way.
With the exception of Rangeley which has a real supermarket, resupply will be of limited selection and expensive the length of Maine.
Salisbury, CT has the worlds most expensive IGA.
Between a couple of meals and a few days of resupply, I dropped nearly a $100 at the AT Deli in NY.
It would probably be easier to list the towns where food is easy and relatively inexpensive to get since there aren't all that many of them!