Sadly my chair is frequently taken for nefarious purposes in my absence. And there's no CPU on the floor, my laptop is always with me. I'm stuck with what I can secure in a drawer.
Well, poppycock. That does make it tricker, doesn't it? Is your hoodie in that drawer or somewhere else?
When I think of my BIB for the office in the winter, my priorities are warmth, water, light, food, hygene and general comfort. That could be a lot for one desk drawer so you need small space stuff. You're off to a great start and there are excellent suggestions here. (i.e. Extra shoes might not work but maybe an extra pair of heavy socks that you could wear like slippers?)