Just because I have really appreciated the help I have received from others here in the past I will do the same and pay it forward by laying it out for you.

Fixed value vgc up to 100 = fuel points (even 4x during promo)

Can be paid for with pretty much any method Kroger allows...even Kroger GC itself. (You can't get fuel points buying a Kroger GC but you can use to pay with it and still get points on your purchase that is made with the Kroger GC).

Maximize 4x fuel points by using a grocery 5x/% card. If you have a Kroger gas station in front of your Kroger you can buy a Kroger gift card at the gas station out front and then use it for the 4x fixed value inside...or the variables (but no fuel points on those). If you are trying to maximize the Discover 5% or Freedom 5% gas station category this is a good way to meet it. Get 500 Kroger GC at the gas station for 5x rewards and then liquidate via fixed 100's for fuel points or a single 500 vgc for only one fee but no fuel points.

Good luck.