Hi Mark,
Even with just a morning session, you will have a huge amount of track time opportunity and the temptation to go from completing your session directly to the queue for the next is overwhelming; my advice, however, is to take proper cooling-off breaks in the privacy of your own allocated pit bay. Pop the bonnet, have a look around, let the car cool a bit, and let yourself cool too!
I've done a few of these Goodwood days; they're extremely well run, friendly and gentlemanly. And as a newbie, you will be offered a couple of early laps with an instructor driving and talking you through the circuit in one of their pace cars. You should take this.
Take tools, spare fuel and any other mechanics' comforts you need. You can unload all of this stuff plus spare wheel etc to the back of your pit bay and hopefully not need it.
Enjoy... It'll be a lovely day.