To my understanding:
The thing is, as a high school student you won't be able to have access to all these fields you have listed, as they are all basically restricted/out of reach unless you have connections and you will probably not be doing anything important or that impactful to the daily workings of the company/place if you even get a position in the first place. You are basically a blank piece of paper (like your resume presumably), so you shouldn't be saying I want to do something in the medical field, law field, or whatnot. Typically a high school student isn't going to get the opportunities to delve into any of your listed fields (that don't reflect the "range" you said, but in reality are really quite competitive and highly regarded, following closely to the stereotyped Asian expectations that go along the lines of "Doctor, Lawyer or Engineer, or you a disgrace"). Anyways, if you really want a job, you can be a receptionist maybe (for a dental practice (closest thing I can think of that is med related that I know a person is in) (don't know if it was through connections or not)), a tutor or a marker for a tutoring centre (quite popular), Woolies, KFC, Maccas, newspaper store or retail work, etc. (Don't remember the age requirements) (anything that doesn't really need you to have work experience, or doesn't deal with too important/responsible of a task). Either way, you are probably gonna be paid at minimum wage, or more often than not, below minimum wage. If you are looking for some work experience you are essentially limited to these options without the connections. Once you have decided which field you want to get into, you will most likely work hard (or you're just naturally smart, and you slack off) for a good ATAR and get into the course at your desired uni, and then you will get internships/placements for work experience related to the field you want to work in.
WHAT????? Then a vast majority of Year 12 students every year would be crying their lungs out if it was too late.