Yes! You can use whatever card you already use for gas (besides Fuelman or Fleetcor cards), and pair your purchase with other promotions. It’s important to note, however, that if you use a rewards card or other promotion, your Checkout 51 gas offer Cash Back per gallon will be reduced to account for the cost of the other promotion.
This adjustment to account for other reward programs is something we've implemented at the request of the gas stations we're working with. They've raised the issue that Checkout 51 gas offers, when layered with their existing rewards programs, can result in them losing money. We do this adjustment as a compromise so that Checkout 51 gas offers work for the gas station, so we can keep them in our app and keep getting you Cash Back. We figured it was better to do this than to have gas stations leave Checkout 51, leaving you with less choice. And you can still stack programs, getting you more savings on gas than just using one program alone.
Please know that when gas margins are tight, you might not see as high discounts - we're not able to offer as much when gas is high! However, margins always recover, so we encourage you to always check the app. No matter what, we hope you never have to pay full price for gas! :-)