I think you would probably be paying for the privilege of shopping among a more responsible crowd than you might encounter elsewhere.
We fill up about twice a month, buying about 15 gallons and the Costco prices are typically about a dime less than elsewhere. By using our Costco American Express card, the gas is about another dime per gallon less. Twenty cents a gallon times 15 gallons times 26 fill-ups per year makes for an annual savings on gas of $78 dollars. This one item alone more than covers our membership.
The Costco American Express also provides a rebate on purchases which amounts to about $100 per year.
Whole chickens are typically $1.09 per pound at Costco but are usually about $1.69 per pound elswhere. At four pounds per chicken and 12 chickens per year, that's about $29 per year in savings.
Perhaps there are items that are not so reasonably priced. Everything we buy is a good deal and we are quite satisfied with the value we get for our membership dues.
For the past several months at our grocery store, whole chickens have been around 77 - 88 cents a pound. I put four more 77 cent ones in the freezer on Monday. I just checked Costco’s site but couldn’t find the chicken and only found organic beef. Costco’s Kirkland regular size green beans and corn is 12/$8.67. That’s .72 each whereas I never pay over .50 for canned veggies.