Did anyone else read From The Mixed-Up Files of Mrs. Basil E. Frankweiler as a kid? You know the story where a brother and sister live in a New York museum for weeks before being caught? I've always felt like I could do the same in Costo and be blissfully happy. Not only can you eat every meal just from the sample tables, you could sleep on a leather couch (from the office department) in a North Face sleeping bag (courtesy of the camping department), and jump on a for-sale trampoline when you got bored.
It's hard picking the best part of Costo, but I'd have to say it's their photo department. They have a kickass website on which you upload your photos and can do all sorts of editing tricks (redeye removal, cropping, etc) before you send them off to their studio with a click of your mouse. Then you just have to wait a day or two before your cheap prints (I think around $0.14 each) are ready. And I've found that Costco's photo center prints better photos than I've found anywhere else-- particularly better than those cheap Kodak stands, where the photos are always super grainy. The Photo Center is yet another jewel in the glittering crown that is Costco Wholesale.