It's great to see that you're already planning to prepare for Year 12 so early on

Just by doing that you're ahead of many of your peers.
For the holidays, it's a great time to
consolidate the things you've learned this year,
rest up, and
start learning about next year's content. I'll cover each one in a bit more detail.
ConsolidatingIf there are any concepts you felt like you don't really understand that well, or have any gaps in your knowledge, now is a great time to patch them up. Having a solid understanding of Year 11 content will definitely give you a leg up for Year 12, as most of the content are built upon concepts learned from Year 11.
Resting UpNow that Year 11's over and it's the holiday, have some time off and rest up

Now is the time to let yourself go a bit, and enjoy the freedom. You can hang out with friends more, go on a trip, play some video game etc.
For holidays, you wanna feel refreshed and ready for the next coming term, so don't overdo it and drain yourself studying too much. Burning out is a pretty common thing for Year 12 students, and it affects them really badly. So you wanna enjoy, and recharge up during the holiday to prepare for the intense year coming up.
Start Learning About Next Year's ContentTo give yourself a head-start, I'd highly recommend looking into next year's content. Gather the resources, required textbooks etc., as early as possible, and start looking through them. Having at least some familiarity with what's coming up will go a long way to help you do better in Year 12.
So to conclude, for the holidays to prepare for Year 12, I'd say rest up and enjoy yourself, but don't forget to remain consistent in your study routine. Go easy on yourself, I'd say about 1-2 hour a day will be sufficient, and if you can consistently maintain that, you'll be pleasantly surprised how well ahead of the syllabus you are when school starts
