Don't be fooled, you can't get away with only one camera bag
. They are like lenses, you need to use the appropriate one for the appropriate job.
Having said that, I've had good mileage out of my Crumpler 7 million dollar home. However it only holds the gear I'm using at the time, my other gear lives in a Pelican case (and a cupboard) at home.
The Crumpler holds a big DSLR with a medium lens attached, my 80-200 f2.8, SB 800 flash (or 300f4) a couple of filters, spare batteries, cables, cards, etc. The two potential drawbacks are the velcro patch which is noisy and it doesn't zip 100 closed so heavy rain could potentially be an issue. On the other hand, I can carry a fleece or raincoat in the top and an umbrella in the side pocket.