C.C.
The last time a few parents in my daughter's class carpooled to a field trip, it was about 30 miles away, or so. The mom who was driving had to stop at the gas station, and I offered her a $20 for the gas, as did the dad who was riding with us, but she said, no, she was going to make the drive anyway and was glad for the company while we drove. So I went to the Starbucks next door and bought Starbucks for her. But she kept saying, "Oh, you don't need to do that!" So... I believe that around here, when you carpool, it's just understood that next time another person will drive, and the person who drove this time will get to enjoy someone else's car the next time. Maybe it varies from region to region though.