I'd recommend a complete year of calculus, linear algebra, differential equations, statistics, and probability. Study programming, even if self-taught. Take micro- and macroeconomics.  Spend enough time bullshitting about philosophy to know what philosophical bullshit sounds like, and take a course in logic (which I missed and miss). Also at least one humanities or sociology class, so that you have the opportunity to do a fair amount of writing.

I think that at the undergraduate level, it's important to build the tools to express yourself and not be overawed by other people's deployment of math and jargon and cynicism. Think of all these tools as a sort of language that we're all groping toward for more precise and powerful conversations.

I also think that the ability to manipulate physical objects and think visually is an important skill, one neglected in the text-based online rationalist community. Your interest in robotics (I see from your user page) might be a good way to build on that.

We're all making this up as we go along. Check citations to make sure they actually support the cited claim. Best of luck!

If you don't feel like you 'get' reductionism on a gut level, the course that nailed that down for me was called 'Computation Structures' - name may vary on your end, but it's a class about how transistors and logic gates are built up through several layers of abstraction until you have a recognizably programmable computer.

As a side note, if you're willing to adopt a more pragmatic attitude towards what constitutes a 'rational' college class, may I suggest searching for information on which majors are highest-paid? :)

This is an interview I conducted with a college professor friend of mine about how to get the most out of education. I have provided a timecode link to the part where we start talking about college.

Edit: An incomplete tl;dr would be: Don't go to a large university, go to a small PUI (Primarily Undergraduate Institution) where the focus of the professors will be teaching rather than research and grant-writing. Teaching a course well is a full-time job, but teaching is the third of fourth priority for university professors. The other answers on this post are probably adequate for deciding what to major in.

Aside from basic math (calculus, linear algebra, probability, ODE, all with proofs), take courses in topics that feel interesting to you just by themselves. Don't count on things you learn being actually useful in real life, and accordingly don't try to prioritize courses by that metric. You'll learn what you need for your job by yourself or be taught at the job anyway, so instead spend this time building up an inventory of things to draw upon for useful metaphors. It's easier to learn what's intrinsically interesting so you'll end up learning more. For real world skills, do some academic research projects and industry internships.

I wouldn't try to fill half your college credits with an informal major in rationality, if that's what you are thinking. Things I would pick up:

• how to prove things - I picked this up taking theory of computation, but a course on something like "introduction to proof" or something in a math department is just as good. The point is to be able to think with mathematical rigor and precision.
• introductory statistics, if you don't already have it. This could be AP statistics in high school, or any social science department will have its own course that covers basically the same content. It is good to have this basic level of fluency, to understand what a p-value is and isn't, how a study is put together, what a regression model is, etc. More advanced statistics isn't really necessary to be a good rationalist in general, but may or may not be useful for research you may want to do later.
• Being able to read and write well is important. Despite majoring in technical things, I made a point of taking at least one course in a humanities or social science department every semester.
• A lot of rationalist ideas draw on cognitive psychology, and to a lesser extent social psychology and cognitive neuroscience. I think you can pick up the important stuff just as well by reading popular books and blogs (psychology is a field where there isn't much distance between the popular and technical understandings). But if you aren't doing that and want to pay the big bucks for a formal class, go for it.

Ultimately, though, if you've got a lot of credits going in, the best use may be to graduate early and move on to whatever you want to do after college. Whatever you want to do after college, you'll learn more of what you need faster by being out there doing it, and you won't even have to pay ridiculously high tuition bills for the learning.