For Arts you should probably also invest in a pillow. Pens and paper are optional really, unless you are going to need somewhere to write deep poetry and don't have access to a Deviantart/Livejournal page.
But in seriousness: A thick pad of that paper with the holes in it, a folder you can put said bits of paper in, possibly some plastic dividers for the folder, and pens. Should set you back about $10 at most.