Haymarket is the perfect place to pick up inexpensive loose fruits, vegetables and herbs on Friday and Saturday. It is located near the Haymarket T stop on the Orange Line and is open year round. You can read more about Haymarket here. The produce you get here will spoil much faster than what you’d get in a grocery store because it is whatever is left over from wholesale distributors [more info here]. Be prepared to eat/cook/can/freeze/dehydrate whatever you buy within a day or two of purchasing. Buying produce here is great if you’re planning on using them for soups or smoothies. Most fruits and vegetables are package-free, but some fruits come in plastic clamshell containers.
Also worth noting: the vendors will try to put EVERYTHING in its own plastic bag. You can get around this by bringing your own cloth bags or simply taking your purchase out of the plastic bag and handing it back (someone else will definitely take it and use it).