I don't have anything on my Rio key, I keep my other keys on their own ring. I throw the other key ring in that hole so I don't have to carry them all day long.
First thing I thought when I read this was "hipster thing to say" and then I realized.... I keep a small local business coffee shop punch card in that cubby which is just as bad................
anything metal will rattle. and my phone wont even come close to fitting. so it has a single paper business card shape loyalty punch card in it.
Nothing, the hole isn't big enough to store anything without sticking out, I don't like the idea of something sticking out of my dash infront of the occupants. Would probably rattle around too.