Here's what I bring...
To wear:
Tri shorts
Tri top
Warm clothes to wear until race start if it's chilly
Flip flops for walking around prior to race
Garmin 305 w/ HRM
Swim:
Wet suit (if cold enough)
Goggles
Colored swim cap provided in race packet
Bike:
Bike with number
Bike shoes
Socks
Helmet
Sunglasses
Nutrition / water bottles
CO2 w/ inflator, spare tube, tire lever
Run:
Running shoes
Race belt
Hat/visor
General Transition Area stuff:
Towel (for marking your area and wiping off your feet)
Water bottle (for giving your feet a rinse off after running in from the swim)