Twice a year, the local Fry's (Kroger brand grocery) runs a promotion where they offer quadruple fuel points for when you buy gift cards. They sell gift cards for all the usual spendypants crap (Macys, various restaurants, etc) but also for things like Home Depot, Lowes, Amazon, and others.
Every dollar spent at Fry's nets your account 1 fuel point. Once you accumulate 100 fuel points, you can redeem them for 10c/off per gallon of gas, at Fry's, or in my area also Shell or Circle-K (each region partners w/ different gas stations). In my particular area (Tucson), which already has among the cheapest gas in the country, Shell and Circle-K consequently also have among the cheapest gas (only Arco is slightly cheaper). As of this writing many stations are selling unleaded for $1.79.
You can redeem up to 1000 fuel points at once, for a $1.00 off each gallon of gas, for a one-time fill up up to 35 gallons (Neither of our cars take that much, but if we bring them both to the station and I quickly move the pump from one car to the other, I can get close to 35). I suppose I could also scrounge up enough portable fuel cans to take the excess, though that might get me some odd looks.
So when they are doing these promotions, I'll buy $250 of gift cards, for stuff that I needed to buy anyway, and net 1000 fuel points, which can get me $35 off my next fuel purchase if I buy all 35 gallons. This is a 14% ROI, so long as I use the gift cards only for planned purchases, avoiding the normal gift card pitfalls. Sometimes I'll even buy a Shell gift card as part of this scheme, and use it up for the gas itself a few minutes later, in some kind of twisted meta-self-licking ice cream cone.
Not only that, but I buy the cards using my Alaska Airlines Visa card, which gives me 1 air mile per dollar spent. These air miles are among the best redeemable in the airline industry (Southwest is better, but AK suits our needs very well) and if you pick the right travel dates you can get a one way ticket from Tucson to Alaska for 12,500 miles; about a $250 value. Therefore each mile is worth about 2 cents; or, this equates to an additional 2% ROI for a short term 16% return on my original $250 spent. Not bad, 40 bucks is 40 bucks.
Unfortunately, they only run this promotion twice a year, and only for a few weeks each time. The points must be redeemed that month or the following, so at best you can get 4 months of the year pulling this kind of scheme. If you already drive a Mustachian vehicle and in a Mustachian fashion, then this can get you enough gas to last the whole year, for very, very cheap.
The rest of the year they only do double points on gift cards, but that still gives a 7% return if maxed out; 9% if I buy them with the airmiles card. It's not enough to make serious dough, but it is really cool to buy gas for 79 cents a gallon just for buying stuff that I was going to buy anyway. However it's a lot harder to spend $500 on gift cards than 250, unless I have a major home improvement DIY project planned.
Of course the pitfalls are all the standard gift card pitfalls.... losing them; hanging on to them too long so the money is invested w/ the store rather than with you; hanging on to them so long that inflation hurts their value; or the most common, simply spending more than you would have spent with cash. I avoid these by buying mostly Lowes or Home Depot Cards, since I generally only go there to get stuff for DIY projects and I always only get what I need for the project, not much opportunity to impulse shop. I also buy a Shell card or two, since eventually I will need to fill up again anyway and they have some of the cheapest gas around here.
