The missing piece
This is my most used piece of gear. If it's 40 or less I put this on to complete the coverage between a hat and jacket. Every day. It's so light and thin you wouldn't think it could be of much value but that is exactly wrong!
For MC use it goes on if the temps dip below 60. It adds a layer of comfort I didn't know I was missing and that leads to relaxed riding making every ride more enjoyable.