From my experience, most of undergrad Econ. courses won't teach you much that will be relevant for FE. There are however, a few courses which I highly recommend: Game Theory, Econometrics, and Mathematical Economics.
In my case, about 45% of my economics education came from Game Theory and Mathematical Economics. Most of the undergrad econ classes don't employ math beyond Algebra 2. That is where Mathematical Econ. comes in...it's a calculus based econ course that delves deeply into static optimization. If not for the economics, you should take this course for the exposure to optimization. I'm not sure if all schools offer a Math. Econ course, but I would imagine they do.
Game Theory is useful in gaining some analytical skills. Econometrics is a must-have - especially since you are likely study some form of Time Series Analysis in an FE program.
If you really want to learn economics in a way this will be useful in FE, try to sit in on a graduate level Financial Economics course. I was fortunate enough to sit in on one last semester and that is where I learned the remaining 55%. The Fin. Eco. course will shed a lot of light on Aritrage Pricing Theory by way of General Equilibrium Theory. The Fin. Eco. course will expose you to the very foundations of Financial theory.
Hopefully this was somewhat useful!