Essentials

Helmet
License
Running shoes
Bike shoes
Bike
Directions to race
Race numbers
Timing Chip and Band

Swim

Body Glide
Wetsuit
Googles (and spare googles)
Google defogger
Swim cap
Swim cords (for warmup on cold days)

Bike

Sunglasses
Saddlebag

Run

Running hat or visor
Speed laces
Race belt
Socks (optional)
Fuel belt

Transition/General

Transition bag
Race clothes
Warm race clothes, if necessary (vest, jacket, arm wamers, wetsuit cap)
Warmup clothes
Sunscreen
Transition zone towel
Floor pump
Electrical tape
Rubber bands
Race food, drink, and salt/electrolyte tabs
Water bottles
Tools and tubes to change a flat
Extra bar-end plugs
Post-race nutrition
Towel for post-race
Post-race clothes and shoes
Garbage bag (for wet clothes)
Medical kit
Trainer or rollers for warmup (optional)
Floor pump
ID