What I wish wasn't taught is Calculus. I suspect many people are drawn away from Computer Science because of all the Math that's required. In my opinion, people can comprehend Discrete Mathematics without having to pass four or five advanced courses beforehand.
I wish I had a better math background, and I wish I was taught both the importance of testing and how to write useful tests.
Linear algebra and numerical methods.
Start a project from scratch (more of the architecture side of things).