Great thread. I'll add my own 2 cents.
Like BobTrips, start by asking what type of pictures you want. For me, high quality environmental portraits, landscapes, architecture and street.
I carry the following
45/2.8 tilt shift
Manfrotto carbon tripod and ball head
about 70gb worth of memory cards
external shutter release
I also carry three bags
ThinkTank shape shifter
Osprey Sojourn 28
luggage locks and lock to secure bags to immovable objects