Tyres, Brake Pads, Brake Fluid, Coolant, Oil/Oil Filter.... Check them all/Change them all beforehand. Remember it's got to get you to the track, around the track and home again.
If you are doing continuous laps then get a brake fluid with a higher boiling point.
In terms of brake pads, I ran 11 laps of the Ring last year on EBC yellowstuffs with no issues and there is still life left in them now. I also ran Conti Sport 6's all round and they too came back with loads of life. (I wasn't hanging about either).
Oh, and have FUN!!!! :-)