Well all tracks I've been to have $3 bottles of Gatorade, so it's not the end of the world if you don't bring any (like a 6 pack of Gatorades for $3 from Wal-Mart).
You might want a 5gal gas tank too, keep topped off. You'll have to make one run to the nearest gas station to fill up. I remember my last track day got really shitty after half a tank because one particular spot I would literally have to feather the gas and take the turn slow because coming out of the corner, if I floor it, my lines run out of fuel and I get bad fuel cut from not having a surge tank. If I had a 5gal jug of gas, I would've topped off, then when that got to 1/2-1/4 tank I would go fill up and fill the 5gal up with it.
Or you can live with the fuel cut and take that particular part of the track slow when you are at or below 1/2 tank, choice is yours.