Play all the instruments. I found that harder. You can communicate with people in so many ways, somehow you can manage to say what you need. But music ... To be able to make sounds with all the instruments, wow! Food for the soul!
This is a challenging question for me. While I would love the ability to speak with everyperson on the planet, I think knowing to being fluent in playing all musical instruments would support me to speak to everyone's hearts rather than their minds. Together with finding a way to increase fun and happiness along the way, too.