We were told to buy a Casebook for every module in 1st year and I can honestly say that I've never wasted so much money on books before. I didn't really use the casebooks, they were all dense and tedious, especially the Constitutional and admin one which was quite easily the most boring book the world ever - it was so bad that whenever I looked at it I would have visions of me sending it through a paper shredder.
This year I've bought just a textbook for each module [apart from Child, not any decent textbooks] and a couple of other recommended texts, plus statute books.
Stay away from casebooks, just go on Westlaw or Lexis and look up the cases you need to. Your tutors should give you lists of articles and further reading which will more than cover the extracts and often mind numbingly dull jiz in a casebook.