“Hot dogs take less than 1 minute to prepare. Italian sausage takes about 2 minutes. Cheeseburgers take 3 to 4 minutes. If you choose to go to the hardware store ‘while you wait’ for your food, I will not re-cook it because it was cold when you received it.”
Actually, the first part of that probably would be considered helpful by customers.
I used to frequent a wagon a couple of blocks from my home. I’d typically ask him for 4 chicken sandwiches (to bring home for dinner) in about 15 minutes, while I went to run an errand. I’d pay him in advance, plus a 25% tip.