No just enjoy the break. The only case I would say it's a good idea to prepare ahead is if you need to catch up on content in subjects you may not have undertaken. For example, to do MATH1131 you will need knowledge of the extension 1 maths content. In that scenario it would be important to do work prior.
Try to use this time between now and uni to work on other aspects such as health/fitness, applying for jobs, resting, hanging out with friends
If you want to a good idea of comp sci I recommend taking CS50 (linked below) and do the lectures + psets. It starts with C like UNSW and is pretty engaging too. I'm currently on week 4 and the psets so far have been pretty challenging but definitely doable + would allow you to basically smurf intro to programming. (Tideman pset 3 is a mega pain though but also fun when you get to it.)