Depends on which desk we're talking about...

Office desk: an empty can, a tophat well as a demo and some Russian paracetamol I found from a pocket of my winter coat.

Home Office #1 desk: the keyboard for another computer, a plant, a bunch of magazines and newspapers belonging to someone else, a roll of kitchen paper, someone else's meds, a cup of cookies, another cup of small tomatoes, a Swiss army knife, a bike computer and a tablet.

Home Office #2 desk: wife's laptop, a bunch of chargers for a myriad of devices, a Kindle, some envelopes full of stickers, others with bills, a lot of random crap, and usually when I'm at the desk, one or two purring felines