Camera bag types
Camera bags come in a variety of shapes and sizes. Let's look at common styles:
Shoulder bag -- This is the most common and traditional style of bag and is available in a wide variety of fabrics, colors, sizes and designs. Shoulder bags offer a good starting point, can be found in not just camera stores but also in department stores and souvenir shops. Quality can vary greatly with these bags, so examine one closely before buying. LowePro, M-Rock, Think Tank Photo, Tamrac, Kata and Domke are just a few of the better known bag makers, but there are others. This style of bag makes a good first bag choice for a photographer who's not sure what kind of bag they might prefer.
Sling bags -- These are similar to shoulder bags, but designed to be worn on the bag and swung around to the shooter's front when needed compared to a shoulder bag which is designed to be slung over an opposite shoulder riding on the shooter's hip. Sling bags can put less strain on the shoulder and lower back than a shoulder bag.
Belt pouches -- These bags are worn around the waist. The photographer positions it around the back where it rides out of the way until the photographer needs access to it. It's then pulled around the waist to the shooter's front and the gear compartment is accessed. These pouches vary in size. Larger ones often come with an accessory shoulder strap since fully loaded these bags can be too heavy for the waist belt to provide enough support.
Camera back packs -- These make hauling a lot of gear easier, but also make getting access to that gear a little harder since the user has to either take the back pack off and put it on the ground to get at equipment, or must ask a helpful friend to retrieve gear. Some shooters prefer to customize regular back packs with foam padding or pouches rather than going to the expense or a back pack designed for photographic equipment. This is a pretty reasonable approach, particularly if you don't have a lot of gear or are worried about a camera back pack making a desirable target for thieves.
Hard cases -- These are better for gear storage than every day shooting, but if you do have gear to store or ship, they offer good protection.
Rolling bags -- These are good for travel or if you have to manage a heavy load. Often these bags can be separated from the rolling cart part and turned into a shoulder bag.
Messenger bags -- These bags try and get beyond the "typical" camera bag look while functioning in a similar manner. "Disguise" style bags work this same approach trying to look like a school bag or book bag.
Chest pouches -- These pouches are designed to carry a camera with a lens mounted and sometimes a small second lens. They can often add an accessory pouch or two. These pouches can team up nicely with a camera back pack so that the user gets easy access to camera and lens for most shooting while still being able to pull other equipment when the situation requires it.