It used to be that anyone who went shopping would have their own shopping bag specifically for that purpose, but the invention of the plastic carrier bag was pretty much the death knell of the shopping bag. The plastic carrier bag had the advantage of being lighter and less bulky than a bag and impervious to rain, unlike the paper carrier bag, so it was bound to prove popular. These days every retailer will pack their goods into a plastic carrier bag for the convenience of their customers and it is completely taken for granted that this will happen.