Rare and Valuable skills worth mastering?

Hey everyone I just read this, which in turn lead me to this and I’m curious as to what are some skills and fields of study that people think fit the category of ‘rare and valuable’.

Not just in white collar environments either, but also considering the entertainment industry, hospitality, trades and so forth.

I’ve noticed anything that involves interfacing tends to have good dividends, especially if you can freelance.

Would love to hear your thoughts.