A calculator with 10 or 12 digits, because sometimes when you're punching in share counts or bushels of grain - or your net worth after joining EliteTrader -you really want to see the billions without having to remember, "did I drop three zeroes or six on that last input..."
You'll see a spiral bound notebook on the desk of many traders. Some use it as a trade log, to record an observation about what caused unusual market activity, or as a journal (this worked, this didn't, my wife left me today, this is my day-end net), whatever. Get a few, you'll use them.
I'm a fan of index cards over post-it notes to scribble down some things I need to remember - what I might want to get into, things I need to get out of and so on.
And if you believe one guy on this site, you should get a big bowl or a bucket (but not your family's popcorn bowl!) because one day instead of getting up and going to the bathroom during a busy market period, he stayed at his desk and shit his pants.