I've had a fabric bag for a couple of years. I bought it in a burst of environmental responsibility. However, my concern for the planet seems to disappear whenever I head into a market, because I keep forgetting I have that bag, even though I keep it in the Rolling Steel Tent's driver door pocket.
Sad looking, but functional
Each time I face the lack of a sack I have the option of buying a new one there at the checkout. Instead, I just load my purchases back into the cart, roll it out to my "house" and load things into the fridge and cupboards. It makes a lot more sense than bagging it all for the short ride through the parking lot.