As for catering/sandwiches... I found you can buy pretty good stuff at shops downtown, so if I stay there, I buy there. No option for a turnaround, but I bring in my catering then.
We once had catering from a very expensive company, paid something like 1200 € for a extensive menue for four pax.
Thought I better change my profession, as making money in that business seems to be very easy. That guy had his van loaded and dropped off at 4 other jets whilst we waited. He collected something like 200€ from each for delivery. 1000€ made in ten minutes...Ice cubes came at 15 €/bag.
Hostie received a tea and biscuits ceremoney without tea and biscuits from the boss. The pax liked the stuff...