Dog food and coffee pay for our CostCo membership. I get the organic Rainforest Blend and it's awesome and $5 a pound.
The added value comes in with:
My undies. 90% of my undies are from CostCo- 6 pack for $9.99
Cheese - we buy the Pecorino Romano, cheddar and Kerrygold sharp cheddar, and sometimes chevre, feta, or if we're feeling really fancy, brie. The regular cheddar isn't a huge savings, but for example, a 4oz of chevre at the grocery store is like $3.50, and a big log (maybe a pound?) at CostCo is like $6, so half price. The Kerrygold is I think $12.99 for about 2#, whereas it's $5 for 7 oz at the grocery store, so again, half price. I try to portion these out and vacuum pack them so that they last a long time.
DH's blue cheese dressing - don't know the numbers, but I know it's cheaper, and no, he won't make his own dressing. Also, his croutons, which he pours on salad like he's pouring a bowl of cereal.
Nuts
Vanilla
Vinegar
Mustard
Wortchestershire sauce
Canned tomato products - can often get organic for the same price as conventional store brand at the grocery
Olive oil
Coconut oil
Shampoo/conditioner/body wash
Allergy meds - a year's supply of the generic Zyrtec is like $15
Protein powder
Toilet paper, detergent, paper towels, cleaning supplies - usually when there's a coupon