Generally you first need to satisfy the track requirements. Some tracks require a battery box, fire extinguisher, helmet etc. Best to check these in advance, as they can vary from track to track and event to event.
Apart from that:
I would suggest good brake pads & tyres. A baffled sump isn't especially necessary but may be worth looking into. You may want to change your wheel alignment to something a bit more aggressive. If you have a loud exhaust (eg above 92Db) you may need to get a silencer.
Generally track days do not have a great deal of requirements.
You may like to pop into
www.aus.s2ki.com and say hello to some local members here. Wakefield Park is a popular track day, and other clubs such as the MX-5 clubs often welcome us along.