In the beginning I had a T90, a few lenses, pair of flashes, quantum batteries, and absolutely everything else I might think I needed packed into a Domke F3x. I took it everywhere. It was bloody heavy. And I rarely used half of what I had in the bag. It took me perhaps four years to realize what a fool I was being, and sold the whole kit in favor of an Olympus IS-1 and no extras. (The wisedom of that move can be found in another thread somewhere, I'm sure.)
When I started acquiring additional camera kits six or seven years ago I also picked up several camera bags. I had a Canon New F-1 in a Domke F3x with a few primes, a T90 in a Billingham 335 with a pair of zooms, a prime and a flash, a Domke F1x for my EOS kit, a Filson carryon for the Nikon F4 and two lenses... It all sounded so good and so organized, and I never used any of them like that. I grab a body or two and a couple of lenses, drop them in a Dockers airline carryon bag I got cheap, and away I go.
My Mamiya 645 Pro resides in a pair of Billinghams; the body/finder/grip/back/lens in the 225 with an additional lens or two plus a back and insert, and a Hadley Pro holds more backs and inserts and another lens. If I'm doing a simple walkaround I grab the 225; if I'm driving somewhere more than an hour away or otherwise expect to do some significant shooting I take both bags. Easy.
No idea what any of this weighs. And there's no heartburning at all over the bits of kit I left at home.