Just because you’re shopping at a discount store doesn’t mean you can afford to ignore coupon deals. Sites like Retailmenot.com offer Costco coupons and money-back deals for specific items ...
you can use a Mastercard or Discover card at Costco.com and via the Costco app. If you prefer to shop in-store at Costco with a credit card, then make sure you have a Visa-backed credit card.