Costco... gotta love that place. Stuff stuff and more stuff, and deals to be had (if you keep on top of prices).
It never occurred to me before, until Susan from http://www.bagsontherun.com/ mentioned it in a post, that Costco doesn't use plastic bags (unless you purchase meat, and this is for sanitary reasons). The rest of your goods must be brought home in used boxes, which they'll provide, or your own tubs or bags that you bring.
We use those purple "bin shoppin' " tubs that you can buy at Superstore - my husband lays them out in the back of the car, and then we fill them from the shopping cart. Many of the things you buy at Costco are in bulk anyway (i.e. flats of juice or canned soup) so bags are irrelevant.
Hmmm... save money AND the environment! Guess we'll keep shopping there :-)