When there's a physical item that goes with a next action, I put it in The Drawer. This is one of the many clear plastic drawers on and around my desktop, with a fancy label on it. It doesn't hold all project support materials--those have their own files or drawers. Usually items in The Drawer belong not to long ongoing projects but isolated NAs that are longer than two minutes. Examples: directions to the party next Saturday, the form about which I need to argue with the insurance company, a letter I want to answer. On the next action list, I put (D) after the next action so I know where the item is. This is working well.