A good camera bag is an important accessory for almost any photographer, whether you are a professional or merely take pictures of places or views that you are fond of during vacation trips. It is important to pick a high quality bag that has room for your camera(s), spare batteries or battery pack, a flash (if you use one), and extra lenses (if you plan to use them for special effects).
Most camera bags are designed with interior compartments specifically for each of these items. And camera bags are designed to carry one or more cameras, as well.
Your camera(s) and camera accessories will usually constitute a significant personal investment. So, first and foremost, you should look for a camera bag that is well constructed and securely fastened together. It should also include a means to SECURELY attach the case to your body or be designed with a comfortable and securely attached shoulder strap. I prefer the latter.
I remember my first experience with an expensive camera. I was young and in the U.S. Navy Reserve on a 2-week annual training cruise to the Mediterranean. I purchased a Pentax camera and inexpensive case, which attached to my belt, at the Company Store and strolled the streets of Naples taking pictures. On my return to the tender, the water taxi bumped and jostled up and down with the waves. When I jumped to the gangway, I watched my Pentax sink to the floor of the Mediterranean! Until next time, Happy Shuttering!