Once a flimsy afterthought in American retailing -- used to lug a purchase home from the store, then tossed into the trash -- the lowly, free store bag is undergoing a luxurious makeover.

From upscale emporiums to midprice chains, retailers are engaged in a heated competition to make the most durable, fashionable shopping bags. They are investing millions of dollars in new flourishes like plastic-coated paper (Macy's and Juicy Couture) and heavy fabric cord handles (Abercrombie & Fitch and Scoop).

Behind the battle of the bags is a significant shift in behavior that has turned consumers into walking billboards for stores.

In a year when some -- like the city of San Francisco -- are working hard do away with plastic bags, others are just as quickly undoing the progress.

And while some of these heavy duty sacks will get second lives as gym bags, purses, and laundry bins -- thus forestalling the purchase of more material goods -- there is a fairly low limit to the number of carriers an ordinary mortal needs. Many, many more bags will undoubtedly get stuffed into closets and stowed under beds ("too nice to throw out!"). And come time for spring cleaning, they will be chucked -- with, perhaps, a grunt of remorse -- into the trash.