Basic load:

Foodstuffs
Fluid
Tube (or tubes if I'm going to be riding with anyone running Stan's NoTubes)
Patch kit
Propane
Cool Tool
Metal Tire levers
Derailleur hanger
Sidewall patch
Pump

Depending on the ride, I will supplement with combinations of:

Clothing
matches
leatherman
trail saw
flask
beer
second helmet
Sony DCR-PC1000
Sony DCR-PC350
Manfroto Superclamp
Monopod
Nikon D2x
Nikon 16 mm 2.8 fisheye
Nikon 17-55 2.8
Nikon 28-70 2.8
Nikon 70-200 2.8
Nikon SB-800 (x2)