This is just my single bike day ride list, but it's a start for others to add to:
Bike
Check tire pressures
Map or directions
Map holder
Pump
Floor pump
Cell phone with case
1 large water bottle, filled
Food drink in other water bottle
Extra food powder
Hammer Gel and holster
Recovery foods and drinks
Recovery pills & vitamins
Helmet
Sunglasses
Various lenses
Sunglasses chamois
Heart rate monitor & receiver
Sprayer
Watch
Shoes
Booties
Gloves
Headbands (2?)
Black poly skullcap
Jersey
Undershirt
Shorts or tights
Arm warmers
Leg warmers
Plastic bags
Plastic cover for computer
Jacket
Wind vest
Sun screen
Eye drops
Chamois cream
Energy bars
Calling card
Credit card
Cash
Driver’s license
Health insurance card
Keys
Spare tubes (correct tubes! Check valves)
Multi-tool
Spoke wrench
Chain tool
Tire levers for other peoples' bikes
Patch kit (check goop)
Tire boots
After-ride clothes
Asthma stuff
Set altimeter
Set Polar sampling rate
Cue sheets
Event paperwork