First get your car up to scratch so it doesn't die on the track day. Redo (if you have to) brakes, suspension, tyres, bushes, etc.
I'd recommend changing your oil (plus filter) just before and after the track day.
Don't use cheap parts on your car. I have first hand experience when the [cheap] front pads on my car died very quickly, resulting in the piston coming out of the caliper as I was thrashing around Oran Park late last year.
I converted the front brakes to R33 4 pots that afternoon in the car park . (For those that went, White/grey R31 Skyline, used a hammer to create clearance for the discs hehehe).
Once you do a track day, you'll be hooked! You'll learn a lot about your car and more about yourself and your driving.
Look after your car during the day, don't redline every gear change if the motor isn't built for it, back off it you have to, etc.
Good luck and have fun. Don't be afraid to go out and have a fang.