I too have many duplicates and many triplicates etc. Of some notions. I have a bag of basic sewing supplies in a class bag that came with a ruler and mat. I usually add to it depending on what type of class I am taking. I have a small mat and ruler and rotary cutter always by my machine and a large mat with a larger ruler and have recently added it's own rotary cutter for there. I was constantly leaving the one cutter behind - it would be at whatever spot I wasn't at at the time! I had an extra cutter just didn't get the aha moment until lots of walking around the room to get the forgotten cutter!