Give Your Friends in the Backseat a Purpose
The driver is responsible for getting the crew to their destination. The person sitting shotgun is in charge of playing music that everyone can enjoy. The people in the back, however, are tasked with what? Handing out snacks? Pointing out silly billboards? Starting a game of I Spy?
Instead of letting your freeloading friends freeload off you, you can put them to good use by having them fill your tank whenever you stop at a gas station. This friend, much like the driver, was too lazy to step out of the car and fill the tank like a normal human being, so they did it from the (dis)comfort of their seat.