The cadets I know had minimal work experience but most of them had some tutoring/retail. They just want someone who is enthusiastic and is mature enough to manage working and university with life. You definitely don't need accounting experience (although it would be helpful if you worked in one). Who sounds more interesting: A student who got 90+ atar, played sports at a competitive level and is very presentable + solid communication skills, or a student with 90+ Atar, worked in an little acct firm, can't talk like a normal person (i.e. no banter) ?
Seriously, most of the cadets I met at uni and during my internship at big 4 are REALLLYYYY chilled kids (i.e. easy to get along with etc). Banter on lync during work is great.