We belong to both warehouse stores but go to Costco almost every week. We only keep Sams b/c there are a few specific items we go there for, plus in a pinch, it's just down the street. First, warehouse shopping overall saves me money & gas & money via my time. I have an elementary age child, preschooler & infant so my schedule is already busy without having to sit & compare ads, then drive around town, get the kids in & out of the car to use coupons I don't have time to clip or stay on top of the dates. I love that I buy dryer sheets, foil, ziploc bags & garbage bags once a year, just to name a few. You have to be able to store these bulk items and we have an additional freezer, but I know I'll never run out of tp or paper towels or other essentials including meal staples.
No one has mentioned Costco's awesome guarantee that any item can be returned for any reason. We've returned little things & big things including fax machine, cell phone & portable dvd player. We then repurchase that item at Costco again. Their customer service is better, they take more forms of payment, have coupons several times a year on items that you really do need. Their offerings of organic products is steadily growing (very reasonably priced too) & they also have their own line of "Kirkland Signature" brand products that are top quality: tp, paper towels, cleaning wipes, dishwashing liquid, diapers & baby wipes.
We have the $100 Executive membership with the 2% rebate that in the end makes the cost comparable to Sam's plus we use our Amex card with a reward points program. On a regular basis we buy milk, eggs, egg substitute, string cheese, shredded cheese, bananas, apples, salad, bread, sandwich meat, frozen chicken breasts, frozen salmon fillets & kids snack and school lunch items. We get our gas there which is usually at least $.05 cheaper if not more per gallon (if only that were included in the 2% rebate!!!) Their package pricing for kids' toys at Christmas is spectacular. Their meat selection & prepared meals is good, they also offer ground turkey. We eat fairly healthy with particular products we can usually get at Costco. I do go to a local market for most of our veggies. They have rotisserie chicken for $4.98 and they're home of the $1.50 hot dog(big) & drink combo! Oprah loves their already-made-but-not-cooked chicken pot pie
If there's something we need, we'll see if Costco has it first, for cost & warrantee reasons. Our future big purchases there will be: digital camera, tv & possibly furniture. They're online too and have a photo place which can be downloaded online as well. We know the CEO's story & believe they do take care of their employees who in turn take care of the customer and are proud to be Costco employees. We love & live Costco. Hope this info helps.