This question made me think that there was a better question to ask.
What did you learn in school that you didn't care about at the time, but turned out to be useful or you had to relearn in the workplace because you had it in school, but didn't retain the information and you needed it? (I mean for software related jobs.)
I think this might help college students identify some of what they really should be paying attention to while they are in school.
I would say at the time recursion and memory management are two things that I shook off in college as things I didn't care for that I ended up needing to practice and relearn on my own time.
For me recursion was taught poorly and seemed almost like "magic" that I never cared to get the full grasp of. The lessons and assignments related to recursion were always trivial and made me write it off and do things iteratively whenever possible. Later, I obviously began to realize the benefits of recursion and put some time in to feel confident having it in my back pocket for whenever it's applicable. Funny thing now is I administer a lot of the hands on programming interviews for my company where recursion is necessary for completion of the problem - all too often I see young candidates struggling to use recursion, apparently I wasn't the only one that didn't master it in college.
Regarding memory management - I did my part to get through my C programming class, but when I went back to predominantly Java it was as if that poorly understood part of my memory was erased. I later forced myself to do some real development in C and get my bearings on all of the basics and beyond. I felt I needed to learn it all for my own sake but doing mostly higher level development I didn't expect to use it - until I started doing iPhone dev where the garbage collector wasn't available. Relearning the foundation saved me a lot of time and headaches in learning the Objective-C way of memory management.
When to settle and just get it done. I Fuss and fret over the stupidest detail and make code portable and reusable to the nth degree when n-1 would work in almost all cases and take half the time.
economics (especially accountancy) and logistics.
We spend most of our time as IT professionals working on software to do accountancy and logistics related tasks, knowing how that works helps a ton.
Sometimes I regret not having paid more attention in Mathematics, however there are many great resources on the web to learn about specific topics so it hasn't really held me back and I think that is probably true for most things. If you're motivated you can still learn the majority of things by reading the internet.
I do think that foreign languages are harder to learn the older you are, I've noticed this myself having started learning French, Spanish, German and Welsh.
Calculus of complex variables. Forgot it all, and had to relearn it decades later when I wanted to develop and also explain some heavy DSP audio processing code.
Psychology. Helped me eventually gain a greater interest in reading about the very human cognitive limitations that can help lead to such things as aviation pilot error and common programming bugs.
Hardware. I should have taken a few classes from the CE and EE curriculum. Being perceived as a "software-only" guy tremendously limits your job opportunities.
Use the libraries and tools that are available!
While fundamental knowledge is critical both for writing one's own code and for assessing the value of the stuff you can find in libs and online, I wish one of my professors had sat me down and said, "this is pretty good code you wrote in 30 hours, but you could've done it a lot faster and just as well if you'd downloaded and used foolib, barlib, and libbaz. Next time, hunt before you peck."
…but then again, we were all still getting used to the Internet back then.
Sorry that this in nothing to do with programming, but:
Singing
Effective learning techniques (mind maps, anybody? Wish I'd had them at school)
Time management
Mnemonics
Spelling
How to get along with others, and conversly, how to argue my point eloquently.
Other things will cmoe to mind later, I'm sure!
I have not needed anything I could have learned in school. All I ever needed in programming was taught hands on. My school did not teach OO and the ONE SINGLE THING I need the most is touch typing - which was also not taught. I can do 4 finger touch typing on my own, but I wish I had had the opportunity to learn it at school.
I started in a profession that is less cerebral than programming. A professor in a programming course recommended against it because, "My brain would turn to mush." Fortunately, I made a career change before too much damage. Majoring in CS or at least taking more courses would have helped.