I’m a big fan of Yubikeys. They’re nice and easy to use and add an extra layer of security. We use them at Code Enigma too, which means that I have a bunch of them for various tasks. The problem then becomes identifying which Yubikey is which. I could have just used stickers, but as I carry my Yubikeys on my keychain, I didn’t think stickers would last very well. A quick enquiry on the Yubikey forum confirmed that the keys are made from ABS.