It is an admirable task.
One thing I would strongly consider how to have the design apeal to the customer but also to the business.
A consumer, myself included will not stand for additional costs when free viable alternatives are readlly avalible. A simplistic but elegant design incorprating brand destinction with overt logo use could lead to a new trend in fashion for the material conscious shopper. It would stop being simply a way to transport purchaces but a decleration of distinction on where the individual shops as they begin to use to it carry lunches or sports equipment … etc.