Mandatory
34 Row oil cooler change oil prior to each even.
Brake Fluid RBF 600/660, Castrol SRF, or better; and a tool to check water content.
Brake Pads Carbotec XP10 front 8 rear or better.
Very useful
Fuel Starve fix, CJM
A track app that overlays video with odbii info.
Prepping your car and getting a good nights rest before you arrive at the track and doing multi day events.
Also
Read these great tips and info.
Autocross to Win (DGs Autocross Secrets) - ATW Home Page
» Track Day Prep Check List Road /// Race Engineering
Race & Track Driving (formerly Win HPDE)
Drive to Win: The Essential Guide to Race Driving (Book)
How to Make Your Car Handle (Book)
After you've read those I can help you spend tens of thousands of dollars on important items like safety because I am just assuming here you are more valuable then your car.
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GTR TT 493Whp/431lbft, Ecutek, Southbend 6puck,Quaife, RPM RollBar 4Point, R888R, JRZ RSPro F(10R/10C) R(10R/6C) 1000f500r inlbs+150inlbs Tender, SPL everywhere.
Full Specs