This may be taking it to extremes, but try dollar cost averaging at the pump for cheaper gas. Obviously this does not work if you have to detour to get gas, but if the gas station is on your route and you merely have to pull over, do this. Instead of filling the tank up, spend a fixed amount like $20, $40, $60 or $80 depending on the gross tonnage of your vehicle. With a fixed amount, you get more of the cheap gas when prices are down. Conversely when gas prices are up, you get less of the expensive gas. On average, gas will be cheaper. Of course, riding a bike, or just getting a smaller car will be much more effective at reducing gas costs than this little trick.
Alternatively you might want to try the hypermiling technique.