1. To potential academic employers you are defined by your job market paper, your letters of recommendation, and by your publications, if you have any. Your formal "fields" aren't that important, nor are your classes per se.Sounds like good advice to me. Some of it I've followed, some of it I still need to take.
2. Pick classes to learn skills and choose your classes on the quality of the professor, not on the topic per se. A quick classroom visit often reveals this quality within thirty seconds.
3. Pick a mentor that you, on a personal basis, relate to very well. This is of extreme importance. If he or she doesn't like you, all is lost.
Also, some advice for being a good mentee.