If you have an American Express card, log into your account online and scroll down until you see the “Offers For You” tab. Many (but not all) will find a Walmart.com offer where you can simply buy a physical or electronic gift card for $79 and get $20 back. (Looks like this, but for Walmart.com). If you ever shop there, that’s an easy $20. I believe you can use Wal-mart gift cards at Sam’s Club and also their gas stations.
Get a one-time $20 statement credit by using your enrolled Card to spend a total of $79 or more online at Walmart.com by 12/31/13.
After you make the purchase at Walmart.com, you should get a confirmation e-mail shortly thereafter. There may be some other deals worth a shot as well such as $5 off $25 at BP gas, $5 off $30 at ExxonMobil, or $10 off $50 at Lowe’s.