My one piano has not much, some unavoidable dust, a mechanical metronome that is too big to travel, misc. music which I regularly relocate to a nearby shelf, a pencil...
But my other piano is a different story. A Bosendofer half-concert grand, very large and shiny, very resonant deep tone, somewhat over-strong, extra keys F-G# on the bottom. Well, it's not technically mine, but being pretty much the only serious student at my university (as I infer from the absence of practicing), I have occupied it since '02. It resides in a large, defunct-chapel-turned-occasional-recital-hall-slash-my-personal-practice-room, with a very nice church organ right next to it (which I also play). When I'm there, there is nothing on the piano except open music being propped open by other thick music volumies (Kalmus ed. Beethoven sonatas don't stay open without TWO heavy volumes, one on each side), a small metronome (sometimes my own), and my pencil collection. Also a watch. There is very little superfluous decoration; a lost music stand; a smal bust of Wagner that used to sit glaring at me from atop a harpsichord until my piano teacher found it and took it away (it had been taken away from him by errant administrators for some lecture or other, two years prior, I found this rather funny); also on the piano misc. spare change for no particular reason.
How could you possibly put anything INSIDE a piano lid? That's absurd.