Whether or not you've gotten on board with reusable shopping bags, chances are you have the plastic variety around the house.
A lot of people use them as bathroom trash can liners. Some people use them to "manage deposits" at the dog park.
Politics of plastic vs. reusable aside, here are a few clever uses for those bags for your next home DIY project.
Instead of buying paint tray liners, place your roller tray inside a thicker plastic shopping bag before pouring your paint. A small piece of tape can be used to hold it in place.
When you're finished painting, carefully turn the bag inside out and throw it away. The plastic bag will take up less space in the garbage than a traditional liner would have. You'll also save water since you won't have to rinse out the roller tray.
How many roller covers do you go through when painting a room? One for the first coat, one for the second coat, maybe a third if you have to stop in the middle of your project to take care of something else...
Instead of throwing all those paint roller covers away, leave them on the roller and wrap them up with a plastic sack. Make sure they're mostly air-tight and they'll still be usable when you get back to painting in a few hours.
When you take your excess plastic bags in to be recycled, they're often made into things like composite lumber. At home, a plastic bag can be made into a fancy wall and ceiling texturing tool.
Simply wad the plastic bag into a messy ball, dip it in joint compound and pound on the wall until you have a light texture over the surface. (Note: This process can also be therapeutic!)