Here is everything that I keep inside my modified Lowepro belt system. This is all I need to do my job. For me, carrying anything else (with the exception of occasionally bringing along my light reflectors) is just extra, unnecessary weight which slows me down, saps my energy, and inhibits my creativity.
The more camera gear you burden yourself with the more time you will spend messing with it, and the less time you will have to concentrate on creating good pictures. Take it from me, this is all you need. Others might even argue that this is too much !
You need to carry two bodies for two reasons. First, if one camera body malfunctions, as mine did last November while covering the "one year later" tsunami story, you need a back up. For more on my broken shutter click here
Second...and perhaps more importantly working with two bodies allows you to quickly change from a wide view to a telephoto view. When my one MarkII went down with a broken shutter and I was forced to work with just one camera body, I found it frustrating and difficult to keep switching lenses to get the images I wanted.