When I lived in the ghetto you could go up to a window with bars and ask for something behind the counter. I wonder if they could put all the food behind bulletproof glass with an attendant and have the attendant slide it through a prison style food tray or something? You could prepay using an industrial grade impact resistant point of sale machine on the other side, and stainless steel floors with drains could be used to wipe the grime down daily and make it easy to flush out anyone camping inside.