I use my diabetes test strip packaging for holding bobbins. I can put about five wound bobbins in each of the little tubes and label them as to what color thread. The lids keep the bobbins from getting lost. Works really well when I'm going to a class or a retreat.
I use one of the metal eyeglass cases for my rotary cutting tool. I can put the tool and extra blades in the case and drop it in my purse. Really convenient when going to class or a retreat.
Also, another item - well, it's not a household item, but it certainly has been repurposed. I use a fairly long (drinking straw length) wand about the thickness of a coffee stir stick with a small brush on one end to clean lint out of the bobbin area of my machine. My daughter uses it on her Gammill for the same purpose. The wand is extremely flexible and I can get into all the nooks and crannies underneath and around the bobbin with no trouble at all and I don't have to take the machine apart.
I got the wand from my gynecologist - they use them for taking specimens for pap smears.