I refuse to assign text books for my courses, which is likely something I should discuss at some point--the cost, the unethical practices of the industry producing them, the issues of copyright, but most importantly, the fact that they can't possibly keep up with how fast and frequently I need to alter my heading as I go.
There is one topic that I'd love to see all my students come in knowing, however: the proper use of Unix command line tools for text manipulation. Today I stumbled on a great little guide, and I'd recommend you read it, then read it again. I couldn't function without this knowledge, and believe me when I tell you that without it, you're not as powerful as you might, and should be.