Plastic bags and plastic film, also known as shrink wrap, should never be put in curbside or transfer station single stream recycling bins because they can jam equipment at the Intermediate Processing Centers that prepare recyclables to be marketed.
A number of participating retailers do have collection bins for plastic bags at their stores. Most of these bags are sent to the manufacturer of a recycled composite lumber that is used for outdoor decking. Better yet, bring reusable cloth bags with you when you go shopping.