I bought a new shirt today. Attached to the label was a sealed envelope with the brand name printed on it. I expected it to contain spare buttons or thread for sewing on spare buttons. However it contained two plastic shapes, about 1cm by 4cm, rectangular except for one end tapering about 1cm from the end. Should I know what these are? I’ve never seen them before.
They might slid in your collar to keep the tips straight.
collar stays? These are brass instead of plastic, but I think they are what you are describing.
Definitely collar stays - keep them because the ones in your new shirt are in open little pouches in the collar and you will likely forget to pull them out when you wash the shirt.
I happened to see collar stays for sale at Target, so if you do lose them, you can replace them fairly easily.
Thank you very much, everything makes sense now. 
I want your life.
It’s simple yet fulfilling.
My ignorance has been fought today.