My parents used to do that once in awhile when they went to a pub. They'd give my brother and I enough for some fries at the restaurant, then we'd have the keys to go wait in the truck. They will deny it to this day, but my brother and I both remember whiling away the time by playing "Taxi Cab Driver". Finally, we'd start poking our head in the door to hound them into getting out of there.
I don't remember how long it was. As a kid it seemed like forever, but it might have only been an hour.