I always buy mine at the Wal-Mart store with a credit card. If the DL AmEx is having a "double miles for everything" (which is quite often these days), I use that. If not, I use one of my mileage earning VI or MC credit cards. Each time, as noted, it is a regular purchase. So no addditional fees!

I don't have a DS to use at Sam's, so last week, I stopped at Wal-Mart on the way to Sam's and bought a gift card (with my VI) to use at Sam's.