What's in my camera bag?

Canon 5D MK2 

Canon 24-70 F2.8

Canon 580EX and two 430EX 

external battery pack for flash

Pocket Wizard's

light diffusers and gels

flash stands and sync cable

Rode videomic

LCD viewfinder 

filter wrenches (for pulling focus)

spare batteries

Canon 1D MK2                              

Canon 70-200 F2.8

remote timer

small Manfrotto tripod

ND4 filter

Cokin filter with two ND8's

duct tape

lens pen

small USB cable

spare CF cards

By no means an exhaustive list. Other essentials include pen and paper, business cards etc. I don't take the filming stuff (mic, viewfinder) everywhere and usually just pack  what I think I will need. I have another holdall which takes my bigger tripod, light stand, softbox, reflector, video slider and large white sheets. Good footwear and the right clothing are also very important.