You can build an obliterator and store somewhat useless (and truly useless) stuff in there. If you find that you need some of the somewhat useless stuff you can pull it back out. When the obliterator can't hold any more you can pull the "flush" handle which will turn the contents of the obliterator into a much smaller amount of coal which you can then use to smelt ore or cam be tossed into your garbage pit if you don't need to smelt anything just yet.