Camera cases come in a very large variety, almost a case to fit any style of camera. From the single camera body/lens case to messenger bags, shoulder bags, and even backpacks the selection is enormous. My intention with this post is not to cover every style of bag, but to stimulate some though while you may be photographing in the field, possibly in crowds and perhaps even in an unfamiliar area.
Carrying your camera without some type of bag outdoors can be problematic.. Suppose it starts to rain? Many photographers have some type of strap in the event that they need to use their hands for something but a strap can cause your camera to sway. Even a belt hook with a large lens can become awkward.
Security is certainly another reason you may not want to have your camera out when not actively shooting. Sadly enough, thieves will look at what appears to be an expensive camera in almost any city in the world. Shoulder straps can be quickly cut and a thief can vanish into a crowd very quickly.
Shoulder slung bags can get heavy depending upon how many lenses that you may carry. It is very easy just to sit them down and once again, a thief can either reach into the bag, or steal the entire bag faster than you may imagine.
Some slim designed backpacks work well when walking around most of the day. Certain packs have a side pocket where one can quickly pull a camera out without opening the entire pack. The weight of the pack (assuming straps are adjustable) can be balanced to make a comfortable carry throughout the day. If you are wearing the pack, it makes it that much more difficult for a thief to steal you equipment. Some packs have a sleeve that will also protect your equipment in the event of rain.
During your next cityscape ,hiking trip, or even a vacation think about comfort and safety with your camera and you will likely come home with more than just some great images!