Glass jars can be used like garden cloches. The hygienist at my dentist decorated several with fancy ribbons and tassels. She used them to store odds and ends like pens and anything that was individually wrapped. I thought that was great. I have adapted the idea.
Bags: Thrift stores love them. They don't have to buy bags if you donate good clean used ones. Our used book stores love them for the same reason as does our local health food store.
Save them up and give your stash to someone who's having a yard sale.
There's a free set of instructions someone on the internet that tells you how to make a welcome mat from them. For that matter I saw several such things made from them on several sites.
One of our local schools takes them for use with their mentally challenged students. Let's just say they send their dirty clothes home with them, tied up inside these bags.
They fit those tiny trash cans perfectly. I have a wooden one. It's a rectangular box with a handle on each end that sticks up high enough to allow me to put the bag handles around it. I also have a black plastic container that I got from the floral department (for free!) at our grocery store. The bags fit those perfectly as well. (The store receives flowers in them.)
I have been known to put one over my hair as a makeshift rain bonnet.
Tie them over your shoes as makeshift shoe covers, when you have to walk in something that's really dirty. Then you can throw them away and you won't have to wash your shoes.
I have used them as lunch bags in the past.
Use them to wrap breakables when shipping them or at yard sales, when you sell breakables.
Stuff cushions with them. This works well for outdoor cushions.
Stuff any kind of Halloween decoration with them, such as scarecrows and the like. When you're finished for the year, you can take them out, and when you store the figure, it will take up less space.
Take at least one bag with you when you're going on a car trip of a day or longer. You can use them to catch all the trash that accumulates as you stop at gas stations and get candy bars and chips. Toss them at the next fill-up.
A long time ago I had a car that sat for a while. It had extended side mirrors. I can't remember which, but wasps or yellow jackets decided the mirror housings would make a great shelter. I went out at twilight when the little devils were just settling in and tied one of these bags around the neck of each mirror housing, just as tight as I could. They smothered, meaning no more danger of anyone getting stung.
We have a pretty good recycling program but I always figure the next person will put that bag in there so I like to reuse them instead of automatically putting them into the bin.