The majority of the CS degree isn't very useful to dev work. Most of what you'll use in your day job you'll learn on your own, or on the job. A CS degree is mostly academic, and also mostly a sampling of a bunch of different domains to whet your appetite.

However there are a few topics I consider essential... operating systems, algorithm runtime/performance, data structures, basic software engineering/design patterns, memory management (seriously, everyone should have a course in C or C++) and functional programming (like Haskell).

Even hacking away at a PHP or Node server, there are times when a bit of knowledge of Big-O runtimes can save you from creating a script that never finishes.