Topic: Core skill set for Ruby on Rails developer

I really want to solidify myself as a Ruby on Rails developer.
What do you think are core skill set required for a well-established Ruby on Rails developer?
Here are some things I have picked up or I am working on.

Front-end: HTML, CSS, Javascript, jQuery
Things related to Rails: RSpec, Cucumber, OAuth
OS: Ubuntu, Windows, Mac OS
Others: Bash
Deployment: Heroku

What else would you add? Especially on the backend related stuff.
I would also appreciate some suggestions as to how to pick those things up because I don't really get a chance to work with backend stuff at all.

Thank you.

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