It's a...bag! No, a backpack. It's a tote for your farmers market loot, and leave it to the San Franciscans to raise the art of the market bag to a science.
This bag, designed in San Francisco by Betabrand, can function as both a bag and a backpack. It's designed like a bucket with layers of pockets and zippers to help you stack and sort your farmers market purchases in an orderly way.
Then, if it all gets too heavy, convert the bag to a backpack for the trek home. Quite a bright idea!