I echo what Gablet said about books, especially first year. You can use the library copies for clarification. You will probably want to buy a DIH just so you don't have to fight over library copies and it is nice to have. You will probably want to buy a dipiro and katzung for 2nd year. I use katzung here and there for more detail. I thought I would do the same for dipiro, but havn't even used mine yet. I know other students that use their dipiro a lot, I just don't have the time to read much.
Class is mandatory the first day of the new qtr and the first day after a holiday. Only the classes that don't matter much (basically every class outside of integrated sequence once you get to qtr 4 on out) will be the ones that take roll. Some of the teachers of these same classes will take roll periodically through the qtr when they see that only a third to half of the class is showing up. Also, teachers of some classes, such as our storied service learning class, would give you points for showing up that were a decent part of the overall points. This happened because otherwise, 90% of our class wouldn't have shown up. You souldn't get docked for not being there, but they have been known to call it a quiz, bonus pts, etc. There are some classes that are mandatory, such as the workshops, and labs, but they will be announced up front in the syllabus. I don't know for sure, as I didn't have the current "Intro to Professional Practice" class, but I am betting that is mandatory attendance.
I feel that attendance requirements and points are absolutely pathetic. After paying 30 grand a year for school, I feel like I should be able to stay home from class if I feel like it. But there are many odd things at our school, like the "strongly advised not to work during school" mantra. I still havn't figured that one out.