Deciding what to carry when shooting, is topic for much debate. Compared to many photographers, I actually travel quite light. I tend to carry what I think I might need, not everything I own and since I don’t like the weight of a heavy bag, I try to keep things simple.
My small bag (for day trips) holds the following: Nikon D200 with 18-200VR lens; Nikon SB600 Flash (only if necessary); Circular Polarizer; spare batteries and CF Card; cleaning kit; lens hood; mount for my tripod. All of this is stuffed into my durable Lowepro TLZ2 bag. The TLZ2 is a light shoulder bag, but there is an optional set of straps to convert it to a chest bag. I use it that way for some hiking or skiing situations.
Probably the most interesting aspect of my kit is the lens. I was never a big fan of superzooms like the 18-200VR, but this Nikon has changed my way of thinking. It allows me to travel light and be ready for most of the situations I face. The VR works very well and allows me to leave the tripod at home for all except the poorest lighting situations. There is some distortion at the wide end, which is easily corrected with Nikon NX software.
Although I do not use the Circ Polarizer often, it can be a useful tool. It works much the same as polarized sunglasses, drastically reducing glare. It also tends to brighten colours and darken blue skies. Be advised, do not wear your polarized sunglasses when using this lens. The polarizer must be adjusted to get the full effect, and you will not be able to do this if your sunglasses are also polarized.
The other items need little explanation. I always clean my lens carefully before an outing, but having a cleaning kit along “just in case” is always a good idea. One or two fully charged spare batteries can extend your shooting time on a long, cold day. I have found that a lens hood seems more necessary on my digital camera, than on my older F80 film cameras. Not sure why, but it might have something to do with the nature of the digital sensor.
As you can see I do tend to travel light. I have other bags for different situations and may add an additional lens (Tokina 12-24), battery grip and flash attachments depending on what and where I am shooting. One tip (got this one from Moose Peterson), always put your camera away clean and in full auto mode. That way you are always ready to start shooting without having to make adjustments. You never know what great shot you might get, if you can just fire away.