sunglasses go in the cup holder
spare change in the ashtray
registration documents are copies, I keep the originals in a safe place (this is actually illegal in Belgium, but I'd rather risk a small fine - if you should happen to fall on a cop that didn't get laid the night before

, otherwise you have 24h to show the original documents in a police station of your choice...- than give the crooks that would steal my car the benefit of getting the registration as well