i used to use a simple backpack with two mesh pockets at the sides for a water bottle and a lens.
inside it will be things like CD player, street directory, and other stuff.
i just sling my cam over my shoulder.
it didn't give my equipment the protection they needed so now i use a Lowepro Mini Trekker AW and dump everything inside.
too bad it doesn't have mesh pockets at the sides for a water bottle though.
and it's quite bulky too, especially when i strap on my tripod on the back.
it's always in the way on a crowded MRT.
My Deuter backpack with my toploader inside plus all my junk.. (extra tshirt - uyou will never know when you need it, water bottle, cleaning kit, gatsby wet tissues - to wipe my face...) and my digital PnS for some candid shots
For a very serious shoot: I carry 3 bags: One for body, one for lens, one for my misc stuff like extra batteries and memory cards. I also carry another case for my tripod. However, I try to put the 3 bags into a bigger bag. I seperate my euipment to prevent abrasion because i walk reasonably fast during photoshoots.
For some simple events or family shots, I just have one bag for my digital camera. Save the extra trouble.