I graduated last year (law), and found Dropbox to be essential. Textbooks and casebooks only made up a small part of my required reading... the majority probably the cases in full* and lots of journal articles. I saved cases and articles as PDFs in Dropbox, and read/annotated in GoodReader/iAnnotate (they kept hopping over each other feature-wise, but thankfully the PDFs were synced in Dropbox so I could switch between apps at will). Being able to export all your annotations and highlights was immensely useful when it came to essay writing and finding the salient points.
I tried pretty much all note-taking apps, and right now I'd place my money firmly on Notability. Evernote is a great central repository for everything you've exported thanks to its powerful filing and search features... a much-welcomed aid to revision. Instapaper was excellent for reading relevant news stories, and I could send them to Evernote if they were worth keeping.
For scanning handwritten notes (unfortunately I did an awful lot of these!), I relied on DocScanner on my iPhone.
Mail was obviously essential (it was the way pretty much everybody communicated at my university... losing email access for a few hours often meant you'd miss something important), as was a judicious use of Calendar (keeping track of lectures, supervisions, deadlines, meetings, sports, you get the idea).
Edit: Essay form varied from supervisor to supervisor. For those I could send a PDF or print-out, Pages was fine. For those who requested .docx and relied on track changes, Word for Mac. For those who preferred handwritten, pen and paper it was.
* I'm not dismissing the significance of casebooks (it's impossible to read every case in full, and in many cases pointless), but they largely focus on what the law is and miss some of the nuanced arguments. My supervisors could tell if I had only read from the casebook/textbook/lecture notes... and believe me, I did try to get away with it.
