I used to have a lot of keys on my keychain and normally kept them clipped to a belt loop with a carabiner. To keep them from jingling too much I used to keep a hard drive magnet that I scavenged from somewhere stuck to them. Not all of my keys were magnetic but enough of them were and the magnet was strong enough that I could sandwich the non magnetic ones between the other ones and they’d all stick together.

It disappeared on me one day, probably stuck to some metal lamp post or something that I happened to brush up against.

I need to check how magnetic my current keys are to see if it could work, but I think if I ever find myself with another magnet of an appropriate size and strength, I might revisit that idea and put the magnet in a small leather fob or something to keep my keys from jingling.