I always pay with credit cards at the pump (i.e. without going into the store) which is very quick and convenient. Even if you pay with cash before you pump, the store will give you change after you finish. As you can imagine, however, it takes so much in and out of the store and waiting in the line twice for each fill-up (unless you want to buy food/drink or use the restroom), I always use credit card. There are two states in the U.S., New Jersey and Oregon, that don't allow customers pump their own gas. In those two states, you have to wait for gas station employees to pump gas for you. However, you can still pay with credit card without going into the store.
You really don't know the US traffic law. The traffic law in US is varies from state to state, city to city. Do you know there are some junctions in some states or cities? There are a sign " NO RIGHT TURN ON RED". So, don't mislead the tourists unless you don't mind a ticket