Aside from completing any homework that you've been given, I would suggest you (definitely) read all of your assigned texts and then take note of the main themes, ideas, characters, etc that you notice in your initial read. Considering the structure of the course, really familiarising yourself with and understanding the texts (and their contexts) you are studying for the single text response and creative response will put you in good stead for the upcoming year (as these are the texts you will study first). At this stage, the most beneficial thing would probably be to read the company study guides (such as Insight) on your prescribed texts as they will help you to begin thinking of your texts in an analytical way and encourage you to develop your own interpretations. If you want to go further then I'd lightly touch on doing further annotations and making your own resources, however, I'd really only start doing this next year when you're having class discussions and have the direct guidance of your teacher.
As someone who went a little overboard with studying in the summer holidays, I would like to really emphasise the need to relax during these holidays. Throughout next year you'll have plenty of time to study, stress and submerge yourself into the world of year 12 - you will need to begin the year refreshed and ready. I burnt out quite badly at one stage this year due to overworking myself and, take it from me, you want to ensure you utilise all of the free time you have. I know it can feel like you need to do the extra work, but having a break will really help to you to succeed next year. Good luck with it all and relax!