I'm going
You can sign up on the Goodwood homepage and put your name down and the car you would like to opt in for the grid/paddock lineup
You can however just turn up and go into the normal carpark.
Baring in mind there are fewer Goodwood breakfast clubs this year and Supercar Sunday is always the biggest I would;
A) opt in
B) turn up fairly early to give you decent parking space, ideally avoiding the field outside the premises