Most grocery stores in the large chains (Albertson’s, Ralph’s, etc) have a plastic bag recycling bin just inside the door, so if you use plastic bags when buying groceries, bring them back next time and drop them in the bin.  Also if you subscribe to a newspaper, you can drop off the plastic bags they come in too.  You can also use these receptacles for plastic bags from any other place like: hardware stores, take-out food, and retail stores.  So just be conscious, any time you buy something and take it home in a plastic bag, save the bag for your next trip to the grocery store.  Another tip, if you’re buying something that you don’t really need a bag for, tell the clerk you don’t need a bag.