I record the purchase & miles driven. The data helps me to track and anticipate when the car will hit certain miles so that I can predict events like new tires, brakes, oil changes and save up for them. For one car, I noticed that premium fuel improves the mileage significantly, making the purchase worthwhile if it’s <7¢ more per gallon.

Also, at Costco, some members have a digital membership card (ie: on their phone).