The idea of bringing your own bag to the market is a good one and is really catching on but many of the reusable grocery bags being sold are made of synthetic materials.  Why not go all the way and get a strong bag that is made from organic materials and printed with vegetable based inks like this one from Envirosax.  Even the box it comes in is made from recycled cardboard and printed with organic soy-based waterless inks.
 
Cultivated as early as 4000 BC, the hemp plant produces the strongest natural fibre known. Hemp fabric is three times stronger than cotton fabric of the same weight. With no known insect enemies and a high resistance to disease, there is no need to use harmful pesticides in cultivation.  A strong eco-friendly alternative.

Color: Natiral
Writing Color: Brown
Measurements: 19.5" x 16.5"
Comes with i's own carry puch.