Of the ones mentioned so far my highest ranking would be learning to learn, saying no, and my first love, programming. Here's one not mentioned so far:

Consulting, the skill of influencing others at their request. (See e.g. Jerry Weinberg's Secrets of Consulting.) This has elements of teaching, but is worth more on the market. It relies on broad experience rather than specialized knowledge. It calls for your clients seeing you as a trusted advisor, relying on you not for deep expertise in their own domain but for an outside perspective, at least a little less tainted by internal biases than they are.

A consultant is often simply someone who is "less wrong" than their client, but to deploy this effectively requires a number of sub-skills: empathy, negotiation, listening, flexibility, networking...

Initially I picked up this skill because I was fed up with wasting my programming skills in the service of employers who seemed to systematically mismanage their own projects. (In retrospect that's not such a good reason to change careers, but that's how I saw things back then.) I went freelance and focused on helping businesses which wanted to improve their project management and development strategies.