What do I do with old coozies? I hate to throw them away.

Use it to hold a shaving cream can and avoid the rust stains or reuse it as a pen./pencil holder. Here's a link with more ideas:

https://www.lazybudgetchef.com/2019/07/12-ways-to-reuse-and-recycle-can-koozies.html

They would be cute around vases or small cans with plants in them such as succulents.

What can you do with leftover koozies? We’ve got 12 fun ideas!

https://www.austin360.com/entertainmentlife/20190703/what-can-you-do-with-leftover-koozies-weve-got-12-fun-ideas

I've spray painted a few and used as holders for odds & ends like pens, nail file, scissors, and such.

Here are a few more ideas:

https://www.qualitylogoproducts.com/blog/9-alternative-uses-koozies-blow-your-mind/

I like the idea of spray painting them. You could then use them for all sorts of things like plant holders, shampoo bottle holders, even pens and pencils.

Here's another discussion about the same topic. https://www.hometalk.com/diy/upcycle/q-what-can-i-do-with-a-large-of-amount-of-koozies-36796850

here are some ideas for you

https://www.youtube.com/watch?v=W8sbTnR7EUY

Duct tape one end closed, fill with ice, then duct tape the other end closed, for an instant ice pack.

Hey Shelley, hope this link inspires you,

https://www.austin360.com/entertainmentlife/20190703/what-can-you-do-with-leftover-koozies-weve-got-12-fun-ideas#:~:text=Store%20breakables%20such%20as%20lightbulbs,you%20buy%20a%20breakable%20souvenir.

HI Shelley. You could use them as furniture moving pads, or to protect any of your glass ornaments. And, if you want to protect posters, cut off the bottoms, and slide a rolled poster thru them. Good luck Shelley. I hope you are well.

cut them up and sew them into cat toys?

You could use them as plant starters or glass packaging for storage (like glass Christmas ornaments. Or kids could cut them and make barbie or other doll sleeping pads out of them.

Hello. A creator of the idea might be to sew them onto your mop rake broom handles or other garden household tools for extra padding to possibly prevent callouses.

following

Great for padding breakables like ornaments.

Hi Shelley,

Wash them and then cover them with a nice fabric, or cut them up and make toys or stuff cushions etc.

https://kustomkoozies.com/different-uses-for-koozies/ some pretty clever ideas here.

This video has some ideas! https://www.tiktok.com/@redeux_style/video/7163756196019588394