CRamming is the BEST thing you can ever do! i find watching tv or dvd's of something stresses me out more, bcos i keep thinking you should be studing! and when i study, its more effective bcos im like look, tomo is your test, you have to learn this. SO cram all you can, and if you are expecting to do well, dont spend the night before your exam watching a dvd, or doing something else you can (peacefully & much more enjoyably) do after the hsc!
But go to bed early, cos i think if you stay up heaps late, you end up procasting and stressing yourself out, so if you're not studing sleep! and wake up the next morning. I can't express how important a good nights sleep is b4 an exam, it will help you on soo many levels.
Goodluck. Go study! lol