What specifically do you see yourself doing? Like training people, and if so what sort (ex. athletes in general, a particular type of athlete, average people), or a physiotherapy, sports medicine type job, etc? Are there any particular certifications you'd like to get in the future? It's rare, but some certs actually do require certain types of classes. Do you see yourself working for someone, or being your own boss?
Anyway, classes I think would be useful: Anatomy, pyschology, a class or two gender (could be under anthropology, sociology, pyschology, since you'd have to be able to work with women as well as men), a food sciences class (which is a bit different than nutrition)...obviously you're not going to be a dietician, but it's good to learn a bit about related fields. Also, possibly a "health education class", probably the easiest class you'll ever take, but since athletic performance is tied to general health, it'd give you some background knowledge. Classes on buisness and finance if you plan to work for yourself. There's also classes that are specific to athletics, I.e. classes on conditioning, strength training, gymnastics...they may or may not be good or useful, but are worth looking into.
