OTC: I would recommend buying the OTC book, even though you don't need it for the midterms, they are helpful as a future reference when you are working and maybe doing future projects at USC. They also help in the disccusion section of the course. The midterms are pretty straight forward memorization.
Biosystem: For biosystem, I would buy the book, it becomes handy second semister especially when Dr. Lubman lectures on the kidneys. I would also buy the little small book review book called, Physiology board review. Dr. Ann said it was a good review book and I agree with him. (1 or 2 questions came from the review book). Second semister of biosystem becomes more physiology oriented and less anatomy, so both books help to clear up some detail.
Biostats: Hmm this is more of a personal call. Some people use it, some people did not use it. It all depends on how well you understand Dr. McCombs lecture and how smart your group is. My advice, form a very smart group. And if you do get the book, I might reccomend you getting Pharmacoepidemiology by Brenda Waning and Michael Montagne, they use examples of what the Biostats book saids. Hope you understand Odd ratio and Relative Risk well. His first few examples, (like the first 5 are relatively easy), but towards the end, he is brutal. The concepts become more difficult and the TA grades harder. So you have to do well at first. Plus go to his break out session, sometimes he gives hints on what is gonna be on the test. The first few test are similar to the old exams but then he change them towards the end. Don't buy any book for the lab, just get into a smart group, someone who knows how to use excel and access.
Pharm calculation: For me, I needed the book. I found the book very useful. Others did not need to use the book. Personal call on that one too. My best advice, practice, practice, practice, practice, practice, practice the problems. They are relatively easy but you can mess up if you don't practice and just skim it over. It takes only about an hour or two in the weekend to do most of the problems for hw. Just do enough where you feel comfortable.
Plus remember your conversion table. Professor is funny, I would go just to listen to his jokes.
Pharmacuetics: Hmm book unecessary. Straight forward. Do the practice test, pay attention in lecture, do any practice problems they give you, study the study guide. VERY STRAIGHT FORWARD CLASS.
The most difficult course I would say is Biosystem for second semister.