Try and arrange your debit / credit card to work in the pumps it's irritating using cash and having to go in and pay first especially if you need change.
You won't have much luck doing that I'm afraid, in recent years they've introduced the irritating policy in most gas stations that you must enter your ZIP code when you're paying at the pump, which obviously won't work if you don't live in the US. Still, I got lucky once or twice when it just said "REMOVE CARD QUICKLY" followed by "BEGIN FUELLING"
