To the OP, only time I'd actually get the books is if they're readings made specifically for the unit (e.g. some Arts units ask that you buy a "reader" from the book store). If you're taking Japanese language units (e.g. Beginner, Intermediate, Proficient and Advanced), you will also definitely need the textbooks, as they get right into it on Day 1; I'm not sure if this happens in other LOTE languages. Most other areas can generally hold off a bit or borrow from the library.
EDIT Part I: I forgot to mention, but Monash Marketplace is a good place to start finding second-hand books. There's also a few more websites you can try if you need them.
EDIT Part II: Lab coats can be bought at the Green Chemical Futures in the first week or so into semester, if you're taking units with labs e.g. Bio, Chem, Biomed, etc.. If you run out of luck there, try going to the bookshop at Campus Centre at any time it's open.