Guest Post: Saving Money at Costco and BJ's Courtesy of Prudent Patron

Before I started couponing, I regularly shopped at warehouse stores to save money. Warehouse stores are cheaper than buying an item full price somewhere else, but I make few purchases that fit that qualification. However, there are still deals to be had at warehouse stores.

The secret to saving money at a warehouse store, or any store for that matter, is to know your prices! Warehouse stores are usually good places to get items that rarely go on sale or have a coupon. Some items I commonly purchase are milk, half and half, frozen fish, produce (when the price is right), movie passes and cat litter.
Once you know what you want to buy, there are ways to get additional savings. I shop at Costco and BJ's. Here are the ways I’ve found to save extra at these two stores:
Costco is pretty basic. If there are items you regularly purchase, like cat litter, from Costco, try to purchase it when there is a store coupon available. If you have the space, buy the limit the coupon will allow. One other way to save at Costco is to stay on the lookout for unadvertised sales, usually in the form of instant rebates. These will be posted in front of the product and will come off instantly at checkout. Last, but not least, how can I not mention Costco’s $1.50 hotdog and drink combo? This frugal girl’s favorite bargain lunch!
If you shop at BJ's, you probably already know that they accept manufacturer coupons and store coupons. However, what is really great about BJ's is they not only allow you to stack the manufacturer and store coupons, but they allow multiple manufacturer coupons on multipacks! For example, if you are purchasing a two pack of soy milk, you can use a BJ's coupon and two manufacturer coupons (one for each soy milk in the two pack)!
It is important to note, I don't actually have a membership to both of these stores (that certainly wouldn't save me much money)! I have a Costco membership and I have several friends with BJ's memberships. We pair up to save extra money! Each store has things the other one doesn't sell. We also find that their prices vary when it comes to the staples we buy. When I go shopping at Costco, I pick up movie passes for my friends because BJ's doesn't sell them. When they go to BJ's, they pick me up a couple gallons of milk because it is cheaper at BJ's. Finding a shopping buddy with a membership to a different warehouse is just one more way to save when shopping at these mega stores!
Do you shop at a warehouse store? What items have you found worth purchasing?
You can see more thrifty and frugal living ideas at Frugal Living.
I'm really happy to bring you this post because this is something I know nothing about! I can't out on my hand how mamy times I have been in a Warehouse Club.  Most of the things that I heard you can save on that are staples we don't use that often in my family so they don't really work for me.  But I know for most families this is good information to have! What are your thoughts? What do you save on at Warehouse type stores?
Thanks Prudent Patron!