Check the gasket on your fuel cap. Its common for fuel to slosh in the tank and weep out the fuel filler.
You'll use a lot more fuel then you think (probably 1/2 a tank) so keep that in mind.
Pump up your street tires to 40 psi cold and make sure you have a way to add air, bleed off air, and accurately check tire pressures.
Make sure you have lots of brake pad and shoe, manually adjust the rear drums, bleed the brakes, and bring extra brake fluid and your bleeder bottles.
Bring a jack, jackstand, lug nut wrench, and a torque wrench. At lunch you may want to swap the tires front to back if the fronts are getting worn heavily. Bring a couple extra lug nuts.
Clean all the crap out of the interior of your car and vacuum the carpets well. It really sucks to have potato chips crumbs blow up off the floor and into your eyes as you're going into a fast corner.
Make sure the seats are well bolted down and remove all the floormats.
Have some consideration for the instructor that's going to be riding in the passenger seat:
Make sure his seatblelt works, is easy to get to, and isn't covered in grease. Get the dash wiring up out of the passenger seat footwell.
Fix any in cabin fuel and exhaust smell issues.
Make sure the passenger door closes and locks easily.
Make sure the passenger and driver's seat sliders work easily and lock in place.
Have coffee, donuts, and beer ready and give the instructor a footrub at the end of the day...