Before I leave the house, this is what I do in terms of just cameras, lenses, and speedlights.
- Put 3 lenses, usually the 24L, 50L, and 85L with hood in the ready position and with both caps off inside my Think Tank Lens Changer 3.
- Put everything else inside the rolling luggage case.
- Aside from this, I have a bigger case that holds my strobes, stands, umbrellas, tripod, monopod, etc. Heavy like a mofo...

When I get to where I need to get to, which is usually at a location where the bride is getting ready, I will take out both my cameras from the rolling luggage case, put lenses on each, typically the 24L and 50L, put 580EXII on each. This leaves 2 slots open in the Lens Changer 3. I'll fill up at least one with another lens, perhaps the 100 macro if the rings are there, or maybe the 70-200 f2.8 IS MKII if I feel that I need a longer range.
I pretty much repeat this for the ceremony and reception. I leave the rolling luggage bag inside the trunk or by the DJ, etc.