Over the years, I've played around with a couple of systems. I have a traditional 'vest', but wasn't ever really all that thrilled with the various bulges out of the pockets, etc. I've thought about moving up to a full jacket, but have hestitated because they would be even hotter still in the summertime, etc. I did finally wear the vest on my 2006 Tanzania trip because it was cool enought to need a vest...still don't really care for the chunky-clunky bit.
I've pretty much settled on wearing the vest for warmth ... and an occasional 'utility' pocket to throw a lens cap into ... and have been using one of two different SLR configurations, or one P&S config:
The first is a "Batman Utility Belt" from
Kinesis . Its a bit intimidating-looking, but the belt's width makes it comfortable to wear for hours. Not good for when you're sitting (riding) or when frequently getting in & out of transportation.
The second is a shoulder bag (that I've had for years) that includes a waist strap (keeps it from bouncing around too bad). The evolution of this system was that I needed something that would also allow me to wear a 20lb daypack. Biggest complaint is that its shoulder strap is too narrow, so it digs in. For carrying an SLR around a city (without a pack), it works out pretty well, as its pretty straightforward to sling/de-sling when getting on & off of trains, cafes, etc.
The third is a generic small fanny pack that I wear to the front -- it holds just a compact umbrella, guidebook and a P&S camera. Its small and inconspicuous and it is what I take on a lot of my business trips.
-hh