Student with a question...

I have been stressed over trying to get into a particular class this summer. Unfortunately, I'm a NEW student, and the school won't let me register until the day before the class starts! Today, I finally received a class schedule for the summer term, and being as there are TWO classes set up, I'm thinking that I'll likely get into one. My question, though, is this. The classes are taught by different instructors, and while the actual textbook is the same, I find that there are different required "extras" for the two. I understand that some instructors prefer to use several references when teaching, but do you think it's wise for a student to get more, or only what the outline suggests? Is this an indication that one teaches more in depth than the other? I'm just unsure about what all I should buy. I don't want to get more than I'll need, but I also don't want to neglect buying something that might actually help, either.