It really depends on what you buy. Some stuff is crazy cheap, others are pretty much the same price. If you're buying a single shirt from Sam's you're probably better off going to Walmart. Always check the per-unit price, and only buy what you're sure you will use. My favorite brand of yogurt is cheaper per unit than the great value brand at Walmart, and is almost 50% lower compared to buying it in packs of 4... But it takes up half a shelf in the fridge. But generally meat is just as expensive at Walmart/Kroger, often you can get it cheaper on sale at Walmart/Kroger than you can get at Sam's, and it's already in packages that you can just toss in a freezer.

Also, I don't know if Costco has it, but the Sam's app lets you scan and pay with your phone, so there's no lines for checkout or anything. That doesn't work to use the gift card trick though.