Programming is a great example of a transferable skill. Beyond being fun, and highly useful for solving many mathematical problems (and this is a very broad category), it can be helpful for automatizing repetitive tasks in various areas.
For example, last week I had to convert the imperial units in a document to metric ones. Probably there are other resources for doing this, but with a basic (2.5 months of learning) knowledge of Python and less than an hour of coding I was able to automatize most of the work, saving myself time and probably avoiding errors and tedium.
So, transferable skills: skills that, upon improvement, increase your ability in other areas (and also improve other, higher-level skills).
A basic example would be reading/writing. Knowing how to read and write allows one to access a huge amount of other skills and resources which are otherwise unavailable. A less obvious example would be clear speech (enunciation). Ability to speak clearly improves one's prospects in a lot of different areas (e.g. professional advancement, dating, etc.).
I'm looking for additional examples. Which skills did you find to be most transferable? Did you become proficient in X, and then found this helped you in many other areas of your life? Please share.
(I tried to find whether this was discussed before, and failed; if it was, I would appreciate the link.)