You can use other notes (a good set of exam notes can be very useful in law) to help with your own write-ups and understanding of the cases, but I'd generally advise against not making your own notes in Contract. That's basically because Contract is closed book, and you have to rely on memory a bit more than most other law units which are open book.
You want to make sure you know all the cases well in terms of facts, arguments, decisions and principles (emphasis on the last one) so you can quickly and accurately apply them to the exam hypotheticals. I find that making your own notes helps you to remember the cases better, as when you go through the cases/textbook/lecture materials and put it together in your own words I think you remember it more effectively (as opposed to reading over a set of ready-made notes). That's just what works for me though, some people may find reading over other people's notes quite effective.