Since plastic carryout bags were introduced in the 1960s, people have used trillions of them, and, for the most part, thrown them away. And whether they’re sitting in a landfill, hung up in a tree limb or floating around the ocean, the bags don’t biodegrade, and they’re not going away anytime soon. They’re free to consumers, convenient and cheap for stores to use. But they have joined billions of tons of tossed-away plastic packaging materials and products to cause a variety of environmental problems. And in a growing number of communities, citizens have decided that they’ve got to go.