At our school, like most, you don't have to wear your uniforms for the actual HSC exam. For the first two papers I did wear my uniform. It was partially about the familiarity of getting ready in the morning, and partially the study mindset it gave me for the exam!
For every exam, I got up at about 5am to study before the exam. I'd study for an hour, have some kind of breakfast or OJ, keep studying, and then do a 15-30 min YouTube, social media, whatever session before getting in the car to go to the exam.
The morning study really helped me. The stuff I studied in the morning seemed to be the most fresh for me in the exam. And by study, I moreso mean revise. Like, I wasn't learning new stuff. Just bringing old stuff to the forefront of my memory.