An email message from my friend Ben, regarding camera bags. Keeping some excerpts  for reference.

… My working configuration when i have multiple lenses is to have at least one empty slot in the bag so that i have somewhere to put the lens down so I only need one hand to manage lens swapping (reduce risk of dropping lens too!). If i need to cram more lenses in my bag, which i do when I have backup lenses with me, is to put the least used lenses at the bottom of a stacked compartment. The lens is there if I need it

Good to know. I will have to make an effort to keep an empty slot in the bag to facilitate the easy changing of lenses.

The UD 40 is the largest bag that I’d carry while trying to stay low-profile. I use mine in two different ways depending on what I’m doing.

1. Gear hauling:
I’d probably pick another bag for gear hauling tonnes of gear but I’ve used the UD40 before as a way to pack a lot of equipment into a small volume. In this instance I wouldn’t be able to access the equipment very quickly but I can get a lot of gear from A to B in one bag. Lenses would be removed the bodies and the bodies would go into the two front slots. Lenses and flashes would go into main compartment that’s separated with dividers. I either have the main compartment divided into only 2 or three sections.

2. Shooting bag:
Here, I’d be carrying 2 bodies (no battery grip) with lenses(usually 35/1.4 and 85/1.2) attached. Each body/lens combo would go into one of two main compartment sections. For me, this is the best way that I’ve found for “casual” shooting. I don’t usually carry lights with me for unpaid gigs. It just too much for me to carry. My preference is to carry 2 bodies with lenses rather than 1 body plus a flashes+transceivers+stands

And below is what I do for weddings:

My base kit ( 3 bodies, 5 lenses, 3 strobes, transceivers, 2 light stands)
goes into an Airport International roller bag:
http://www.thinktankphoto.com/products/airport-international-v2-roller-camera-bag.aspx
I also have another big bag for 2 AC-powered strobes and a 48″ lightstand bag.

When I’m actively shooting. I’ll be using a chest pack + 2 skin pouches attached onto the “wings”: The pouches were made to carry bodies only, but i use them to carry lenses instead (each pouch can hold up to two lenses, but i leave an empty spot in each of them to facilitate lens switching…)….I’ve also recently found out that you can fit a body and a prime lens attached into the pouch….very handy when you’re shooting three bodies at once. Yes, I’ve run out of hands! 🙂
beltpack: http://www.thinktankphoto.com/products/change-up-belt-pack.aspx
(I totally look like a photo dork with this on, but this feels more
comfortable to me than just using a belt with pouches)
pouch times 2: http://www.thinktankphoto.com/products/skin-chimp-cage.aspx

My active set up doesn’t let me carry strobes, but If i need to I can wear a backpack to let me carry more stuff. So now i look like an even bigger photo dork:-)