Ok, the YMMV part.
This is a post mostly for people that has. Giant that participates in Gas rewards. This week (up to Thursday 1/25/18). I can buy a $100 eBay GC and get 10x the rewards points. That means I'd get 1000 points, which equals to $1 off a gallon, UP to 25 gallons.
I fill up 25 each time (car and gas jugs) so for me, it equals to $25 off. I do use my Amex Blue Cash Preferred ($95 annual fee, but I can max out the 6% grocery alone at $6000, getting back $360, which converts that fee) that gets me 6% back, so that's another $6 back. Plus when there's an eBay promo of % back or $ off, you'll get even more value.
I'd at least buy $500 EBay GC anyway, so I'd have $5 off a gallon (I can use the $2+ that's left per gallon on the next fill up). So yeah, a little work, but the Giant gas rewards is great for us. Haven't been buying gas locally (on vacation out of state/country not included) for 6+ years! It's not always gift card, usually grocery, but it works.