Essential:
Road gear off (inc side-stand).
Plugged handlebar ends.
Balls on the end of your levers.
Race numbers.
No sloppy bearings in the wheels, swingarm or steering.
Brakes that work (!).
No loose/missing spokes.
Throttle that returns by itself.
From there, you'll get a lot of 'advice' about a million things that you "must" do. A lot of it will be good stuff that will help you get around the track faster, but none of it is essential.
You're far better off just getting out there and having a go on a average bike, than you are spending the next ten years making it immaculate and pristine and not actually racing...