I know this piece of MDF next to my palette looks a bit rubbishy. But it's one of my most useful gadgets, and I made it myself ! It's my version of a mahl stick , or a hand rest to stop your wet painting getting smudged when you work on it.
It consists of a piece of about 12 inch by 4 inch MDF with a couple of smaller blocks glued to either end. It just clears your working area and gives a large surface to rest upon. This has it's limitations of course but for a home made gadget I think it's very efficient.