Pushing your fuel purchases aside for one day isn’t going to have any impact on the oil companies (although, amongst the laughter, you might hear impassioned cries of “Oh, please, Brer Fox...”).
If you’re serious about doing them damage, start walking to places instead of driving, then buy yourself a deadly treadley and ride to places that are an unreasonably long walk.
Then send emails to all of your mates explaining that unlike the previous recommendation this will actually work, keep working in the long term, improve their figure into the bargain, save them money, boost their sex life (through being stronger, fitter and more agile) and help them to meet people if they have no sex life. IOW, it’ll help them to do everything that 90% of their email is (and apparently always will be) constantly urging them to do.
The straw that crushed this camel was getting a no-fuel-day email from a lass (my favourite random) who has no car. Lead by example? “I didn’t buy any petrol on that day” or any other day, d’oh!
BTW, James Dumay, look here to see a serious split keyboard which can be readily made for less than half the price of a Natural (even if you have to sacrifice two boring USB keyboards to do it) — or if you want something fancier, try this.
If you want to try it out before cutting, just plug two USB keyboards in, hang them from the chair, and start typing. With a little surgery, you can probably do stuff like have multiple common keys (shifts, spacebar, enter, numpad, tab) on both sides and/or under your wrist(s). The assorted Shift and Lock keys will still work because they’re interpreted by the CPU, not locally. If you have keyboards with “media keys” a nifty use for those (extra geek points) is to hook them up to pedals or kick-bars and define them as “Save”, “PageDown” and other stuff that it makes sense to do while leaning back or getting up to go.
Since you can no longer see the Lock lights, you can make them do cool Cylon-like scanning tricks instead, with a small kernel patch to disconnect the keyboard driver’s shift bits from the hardware.