If your plane is departing from Honolulu in the morning then if I’ve done my calculations correct, you should be arriving at Sydney in the morning. If that’s the acse for you then i highly recommend that you sleep as much as possible during the flight. This will reduce your jetlag tremendously.
But if you are landing at Sydney during the evening or night time then don’t sleep more than 2 or 3h because upon arrival if it’s night, you should go to sleep and not stay awake. So even if you’re good at adjusting your sleep schedule, i still don’t recomend sleeping if you’re arrival time at your dest… is at night.
Sleep if you’re arriving in the morning at Sydney.
Don’t sleep much or at all if you’re arriving during evening or night.
Other than that there’s not much you can do… maybe make a good use of their In-Flight Entertainment System… (Don’t know of they have one on A330 or even if it’s good, don’t judge, I’ve never flow ln with Qantas)
Edit: See if you’re allowed to speak with the pilots, take walk down the aisle. Sitting still for consecutive hours is dangerous and lastly stay hydrated as the air is very dry at higher attitudes. Maybe talk to other passenger passengers?