I think one of the most important art supplies for painting is a desk. "You've got to have a desk." You might ask "Why do I need a desk?" You might even say, "I can paint at my kitchen table, on my lap or in bed, on a breakfast-in-bed tray". There are a lot of problems with painting in those locations. If you have a desk where you can lay out all your supplies and leave them set up, it makes your painting process much easier and better.
I am going to go one step further in my thinking about the desk for painting. I've decided for myself, I need to have a clean desk. So I have cleared off the piles of papers and finished paintings and odds and ends that were crowding up my desk top and stored them approximately where they belong. It's very refreshing to look over at my desk and see open areas on it. It makes me very happy to have a clean painting desk and you know what I always say, "If you have a desk and some watercolor paints, a few brushes and a pencil with an eraser and a piece of watercolor paper, you can paint a nice painting, it's not rocket science."