In my "bike shop" the only consumables are lube, grease, patches and cement. I buy everything else as needed. I can go through a bunch of tubes in a short time, and then have the last one bought sit in a box for a year. I happened to have a cable set when I needed them recently, and it was Campy that I needed too, I'd bought it to swap out cables but then never did. If it ain't broke don't fix it. I do have spare 10 speed chains, but that was by an accident. They'll last me years. I have my junk box, and was able to pull out a pair of brake pads that were still good the other day. But in general there is no reason to stock items in case you'll need them, that case could be anything and you can't much predict it.