Try to get there by 11:30. Later, expect to be cheek to jowl with neighborhood regulars, students, and, now, tourists who have read about it. I know this as I ate there a few times but also walked by it many times and it was always crowded around 12:00 to 1:00. If you get there after 12:00, expect to slowly move toward the bar in a crowd. When you get there, you have a choice of 3 or 4 different sandwiches (prosciutto, salami, etc.,) on really good crusty rolls and small glasses of wine or prosecco. The sandwiches aren't big, so if you're hungry get three, if not so hungry two or one will do. You can sit on the steps, stand in the Campo or maybe find a space on one of the barrels outside the shop to rest your wine glass and food.