I sit in the car with the children, before we go in and review what I expect. It boils down to cooperative, polite and obedient. I give details for the younger ones such as "I expect to correct you only once." I put on the line what is at stake...."You will never see the light of day....not really, but they walk in knowing that good behavior means dessert and bad behavior means a long week.
We don't take all of ours out very often, because of the cost. Last week we all went to the Chinese buffet for Tom's birthday, and everyone was just fine except the baby. He yelled a few times, but the place was almost empty (a Monday evening), and we were back in a corner.
I think parents have to combine expectations for good behavior with some common sense about what is just the WRONG place to be, especially with a toddler. Takeout can be a good idea :-).