Earbuds in keychain case
Since I listen to music on my phone I like to always have my earbuds with me so this is my solution. I have a keyless entry car (VW Tiguan) so I just move my hand near the outside door handle to lock/unlock the door, and to start the engine I push a button on the dash. I never need the car key in my hand to operate the car, just have it with me. I have a small keychain case (pictured above), about 3 inches square with a zipper, that has the car key in the bottom (which is never taken out) and my earbuds in the top. (I always have my phone in one pocket and my key case in another pocket, so listening to music is always available to me.)

When I walk the dogs I listen to music primarily now with wireless earbuds that have to be charged.

In 2016 I moved to a house with a keypad doorlock, so I don't even carry a house key anymore, but a case is still in my pocket.