Don't worry about octane boost, playing with tyre pressures, or screwing with anything on the day.
Fill it full of fuel, set your pressures at about 40 before you leave home and simply concentrate on driving. That will be a big enough learning curve on the day without having to worry about everything else.
As Taz said, read the CAMS regs, and also the event supp regs, as some hillclimbs (especially up here) have certain extra things they need the car to comply with.
And don't forget to have fun.