Customizable Plectrum ([guitar] pick)
Every player has their own preference for pick thickness, shape and material. This design features tapered thickness, variable corner radii and optional hole for hanging on a keyring, necklace, etc.
UPDATE: Added a second STL file, modified with a center hole and a notch so it can be clipped onto a cord, whammy bar, belt loop or wherever it's convenient. You can even use it as a baggie tie!