It's actually less of a problem if you have a lot of kit to carry:
2 cards in each camera - removed, images downloaded, replaced in cameras and re-formatted as part of workflow - kit doesn't go back into bags until it's been cleaned and checked.
Main bag:
2x D3 bodies
lenses: 17-35; 24-70; 70-200
2x SB900 flash
SU-800 commander unit
12 spare cards
4 spare EN-EL4a batteries
Cleaning-kit (if not in ancillaries bag)
Ancillaries bag (only on overnight jobs):
D3x Body (if not used for main task)
Lenses: 14-24mm f/2.8; 50mm f/1.4; 85mm f/1.4; 105mm f/2.8 Micro-Nikkor (if not used on main task)
4 spare EN-EL4a batteries
Battery-Charger(s) and leads
flash-remote lead
electronic cable-release
Spare flashguns: SB900; SB800 & SB80DX
2x Pocket-Wizards
12 fully-charged AA batteries
12 disposable AA batteries
Cleaning-Kit
1x Spare t-shirt, underwear and socks shrink-wrapped in poly-bag
toothbrush
disposable-razor
Prior to a job, all kit is laid-out on the floor and packed according to a packing-list I made up years ago and amended as new kit was added/removed.
That way nothing gets missed.