Plastic bags were the answer environmentalist used to love because we could save soo many tress by no longer using paper bags.   If you use cotton bags you run the risk of cross contamination from having juices from raw meats one week contaminating the veggies of the next.  Has to be true seen it on the news.  Don't dare wash them after each visit because you have to conserve water you know. 

The answer is we dont really have one yet.  Personally I would like to see those bags a little thicker to get more use out of them, then maybe find a way to shred them into an insulation material, or used to make a cotton/plastic clothing material to increase durability.  

Those bags are really a drop in the bucket when you look at all the disposable plastic goods we have in our daily lives.  Charging to use them is putting a band aide on a severed arm to stop the bleeding.   Its a good thought but in reality it wont stop the damage that has already been done.