Culture. The fact that it doesn't matter what the company says their culture is and that their culture is defined by the behaviors that they do and don't allow in the workplace. Culture can vary from team to team and department to department.
Deadweight. The organization is going to be full of dead weight.
Get ready to feel under-appreciated and under-valued.
- bash + GNU coreutils; seriously, take the time to be able to write helpful bash scripts which can run basically anywhere.
- git; use it even when you're not pushing to a remote. Add helpful aliases for everyday commands. Build a good mental model of commits and branches to help you through tough merges. ( my ~/.gitconfig: https://gist.github.com/jeaye/950300ff8120950814879a46b796b3... )
- Regex; combined with bash and your GNU tools, a lot can be done.
- Vim; modal editing and vi-like navigation can blow open your mind. Explore the existing plugins to accomplish everything you want to be able to do. It's all there. ( my ~/.vimrc: https://github.com/jeaye/vimrc )
- Functional programming; if you're new to this, start with Clojure, not one of the less-practical languages. This has made such a huge impact on the way I think about code, write code, and design code that it's possibly the biggest one here for me.