We prefer to shop at Kroger grocery stores - which can be hard to find while traveling. We get 10 cents per gallon for the next gas purchase with every $100 spent in the grocery store. Nice thing is we can often buy restaurant gift cards and get double points for our next fuel purchase.
We have the Pilot/Flying J RV Plus card and get 6 cents discount on gasoline, we also get a discount on propane.
We keep a Walmart credit card to use only for fuel and the 5 cents discount on gasoline if that is a last resort.
We haven't figured out the discount scheme on the Exxon/Mobil credit card. Some locations no discount, some 3 cents, some 6 cents and yesterday in New Jersey - 10 cents per gallon. Note - the station was offering gasoline for 2.19 cash and 2.29 credit. We got 2.19 with the Exxon/Mobil card.
We also use the Gas Buddy app and often find driving a couple blocks off the interstate or main highway can save us 5 or more cents per gallon.