Yeah, Year 12 half-yearly's are towards the end of Term 1. I would suggest you study hard these holidays (but to reiterate what pLuvia, have a life too!) because once school starts again, you're going to be flat out.
Read all your English books that you have to read, at least once. Find your English ORT's. Write notes on what you've done so far in each subject. If you feel like it, maybe even start studying ahead.
I noticed you do maths - maths half-yearly's, yearly's etc. test EVERYthing studied so far in the HSC AND Prelim course - so revise Prelim.
But have fun too! Because like I said, once school starts again, there ain't no stopping until the HSC is over.