When we hung with my friends with the Chinese restaurant, we'd take their son (4 or 5 at the start) darn near anywhere. Two rules covered a lot of ground.
First was car behavior, told him once and he repeated it from memory:
Get in, sit down, shut up, hang on.
Second was restaurant/other adult amusement behavior:
We'll take you anywhere we go, as long as you act like a grown-up. If you want to act like a kid, you can stay at the restaurant by yourself, while we go have fun.
Never had to explain that a second time, either.
He was a great straight man, too. Like the time we went to Fuddrucker's, a great burger joint near Hooter's. We went close enough to the latter for him to memorize a lot of details. When we got back, dad asked where we went, and he told him all about the trip to Hooters.