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, and the only key I have readily accessible is my house key (I plan to have keyless entry for my house soon so the house key will no longer have to be accessible either). I always have my phone in one pocket and my key case in another pocket, so listening to music is always available to me.

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.