Why are you looking for additional examples? I think it's a good question, but clarifying why you're asking it may lead to better answers. If you're looking to learn transferable skills yourself, then our suggestions can be more targeted. Or if you're looking to make a list of a general audience, then our suggestions can be more general.
To give a very general example: basic mathematics is so transparently essential. Intermediate and higher level math can also be extremely helpful, depending on what problems/activities you're tackling.
Good point. I'm trying to cast a wide net, to see whether there are highly transferable skills that I haven't considered before. There are no plans (yet), this is simply a kind of musing that may (or may not) become a basis for thinking about plans later on.
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.)