I'll comment on it, though everyone disagrees with me about this.
I think the most important thing that helped me was physiology. It doesn't have to be human physiology, the basics of the organ systems is all the same. The reason physiology is important is because there is a BROAD amount of information that they could possibly ask about, and you just don't have enough time to study it all.
Biochemistry would have been useful for me. I didn't take it before the MCAT, but I recommend it. It helps for sugar chemistry, glucose metabolism, etc, that could show up on the MCAT.
Molecular/Cell biology is useful for passages just cause I had several passages on the MCAT that explained things I learned in cell mol. Basically, they were topics you could have figured out from the passage, but I didn't need to cause I already knew them. Take what you want from this. I don't know how other MCAT administration are, cause I only took them once.
On the other hand, MCAT genetics I found was easy and there's not alot you need for it. Mendelian genetics? You probably saw it in intro bio, that's all you need. Pedigrees? I read up about them before the exam and found them very easy to grasp.
The amount of microbio that could show up is minimal. Know the very very basics.
I certainly think it is possible to get a great score without those extra classes. No matter how you go you will need to prep extra for the MCAT. Also remember that the most important subsection score is the verbal, which has nothing to do with science. Further, lots of questions in the science sections will have more to do with your reasoning abilities and strategies.
Good luck!
