Here is a simple idea. Have you ever thought about saving that perfectly re-useable paper bag you got at a fast food place? Not always but sometimes that fast food bag is clean. Should you just throw it away after using it for a total of five minutes (sometimes less)? It just seems wrong to waste.
Instead, save it to pack a lunch one day. I prefer reusable lunch boxes but sometimes you can’t pack in a lunch box because of bulk, like when hiking etc..
Always look for ways to reuse.
…and when appropriate, tell them to skip the bag.