If people would allow the natural flow to operate of people going through the line, ordering, getting their food, sitting down and eating, then leaving then there would almost always be seating for people.

We just had this happen at R&R Barbecue. We and several other people had gotten our food with nowhere to sit. Some guy is occupying a whole big table by himself. My wife tried to ask him if we could sit at that table and eat real quick, he said his wife was in line and that we were out of luck. (His wife was at the back of the line in a packed house. We easily would have been done and out of there by the time they got their food.)