Get the TrueEarnings Card from Costco and American Express for no annual fee with your paid Costco membership. The best perk it offers is 3% cash back on gasoline at U.S. gas stations, including ones at Costco (up to $4,000 in purchases, the 1% after that). Plus, you'll get 2% back on restaurants and eligible travel, and 1% back on everything else, including your Costco purchases. The cash back comes in the form of an annual reward coupon. On top of that, it offers 0% APR for the first six months (regular APR variable 15.24%).