Even as a single guy, I still manage to use my membership pretty often here. Costco is perfect if you are buying large bulk things for a party or even for dry grocery items you don't mind having a lot of.
Costco has their own brand (Kirkland Signature) which is good quality for a little less than the national brands. You can buy almost anything at Costco!!! I bought very nice tires for my car and they do complimentary rotations and repairs which pays for the membership itself. I even have bought clothing here, nothing fancy, but casual things I can wear to work that are much cheaper than going to the mall!
Another bonus here is the food court! I don't know how they make money on $1.25 ice cream or $1.50 hot dogs and soda, but the food is really good and won't bust your wallet. I've joked with people that I might just go there one day for lunch, and I'm kind of serious!
Just a few tips: While they do accept Debit/Cash, for credit cards you will have to pay with American Express. They do offer a AMEX membership card which gets you cash back and the annual fee is the same price of a membership. My mom has this card and always gets a few hundred dollars back at the end of the year, thus paying for her membership and more!
Costco from what I hear really treats their employees well and it shows! Everyone is very friendly and seems to enjoy what they do. Don't be shocked if you wait a long time in line on weekends because it will get very busy and might make for a frustrating shopping experience.