If you don't mind spending more time at the gas station, but you want to save money, only fill your car half full. Half a tank of gas weighs over 25kg and lugging that around actually affects your fuel economy. But don't let your tank get too low otherwise it'll pull all the crap out of the bottom of the tank through the fuel filter.
Also, when you do fill, make sure you fill enough so that you get the maximum loyalty points. E.g. if your card gives you loyalty points at $20, $40, $60 dollars, etc, don't put $50 in because then you've spent $10 for no loyalty points; you'd get the same number of points as putting $40 in. (Note: not all loyalty points schemes work the same way).
