With Special thanks to Mike Whitney for compiling this list

Having forgotten something at nearly every driving event I've been to, I decided to get, ah, organized.  Feel free to steal / copy my list and make it your own!   This is based on a list I copied from a BMW website.  Items I consider optional or that are not always needed are in italics.

Getting there and getting in
Registration materials Radar detector
Maps / Driving directions CB radio
Hotel Reservations Cell phone
Helmet GPS
   
Clothing & Personal
Jacket Snacks
Cap Water / drinks
Sunglasses Cooler
Suntan lotion Cash, Credit Cards, License
Lawnchair Pens and Notebook
First Aid Kit / bandages Towels
Camera, film Blank checks
Umbrella Rain suit
Lock and cable Extra shoes (if raining)
   
Supplies and Disposables
Garbage bags Duct tape
Brake Fluid Anti-Seize, Locktite, WD-40
Motor Oil Towels
Window Cleaner Work gloves, latex gloves
Paper Towels Bungee cords
Tie Wraps Fire extinguisher
Headlight tape Transmission fluid
   
Tools
Flashlight Funnel
Sockets, ratchet, extensions Fluke Multimeter
Test wires / leads Tire Pressure Gauge
Shock adjusting knob Tarps
Floor Jack Torque Wrench
Old Blanket Breaker Bar + 17 mm socket
Wheel Chocks Knife
12 Volt Air Pump  
   
Parts
Race Tires Spare Nuts and Bolts
Spare Lug Bolts Repair Manual
Electrical Connectors and Tape  
   

Track Event list and optional

Registration materials
Technical Inspection Forms
Helmet Release
Spare Brake Pads
Spare Rotors
Extra Brake Fluid, 1 or 2 Liters
Brake Cleaner
Brake bleed hose and wrench (7 mm)
Spare Brake lines
Jackstands
Long pants
Long-sleeve shirt
Battery Operated Drill
Drill Bits
C Clamps
Jumper Cables
 
 

To-buy list

Rain boots + shoe covers
Portable Airtank
Turkey Baster (Brake Flushing)
Spare Fan Belt
Pressure Bleeder
12 Volt Trouble Light