The whole premise of don't by gas on X day or even any short period of time is just plain flawed,
First if you plan to not buy it that day you know your still going to buy it, just the day before or the day after or whenever. Some of us avoid buying gas on Sundays as is, doesn't make a particle of lint of difference.
It was suggested on another forum that if we drove no more than 55mph voluntarily for a month it would actually have an effect.
Second if everyone got together and really did something that effected the amount of gas being consumed and profit in sales etc. what would be the results? an enexpected spike in supply causing an increase in storeage costs to the oil company due to the unexpected surplus, along with a loss of revenue so then what? as was mentioned earlier they just readily pass that cost along to thier customers right? I may be thinking wrong here but it seems to me an effective temoporary boycott of buying or using gas will only result in an increased price at the pump after the boycott.