I often have to leave on a moment's notice to shoot photos: local breaking news, last-minute calls to shoot plays or concerts, and that sort of stuff. It's extremely helpful for me to keep my camera bag packed with my most commonly used equipment so I can grab it as I'm heading out the door. This equipment covers 90% of my needs for most shooting, and it lives in my camera bag:

• Nikon D700 + MB-D10 + charged EN-EL4a
• Nikon 80-200mm f/2.8 AF-S
• Nikon 17-35mm f/2.8 AF-S
• Nikon 50mm f/1.8 AF-D (soon to be replaced with the new AF-S version or the Nikon 28-70 f/2.8 AF-S)
• Nikon SB-800 + batteries
• Blank 8 GB CompactFlash card
• Roll of gaff tape
• Microfiber lens cleaning cloth
• USB card reader

I can grab my camera bag and head out the door even while I'm still on the phone getting the photoshoot's details. I'd recommend that any photographers who shoot frequently (particularly photojournalists) put together a similar "photo go bag".

Note the gaff tape on that list - I never, ever go on a photoshoot without my roll of black gaff tape. It's immensely useful.

Depending on what subject I'm shooting, I might need some additional equipment. The most common things I grab on my way out the door are a second body (the Nikon D7000; I keep the battery charged all the time), any of my fast prime lenses, a second flash (Nikon SB-600), a macro lens, or a fisheye lens.

Incidentally, all this fits nicely in a Domke F-2 canvas bag. I highly recommend that bag - it's durable, pretty waterproof, large, and comfortable.