SLR cameras are top notch cameras and for that they are also quite expensive. They have add ons that can enhance their photo capturing capability. So it it is just fitting that you get a SLR camera bag for your SLR camera and all the other equipment related to your camera.
The camera itself and the accessories should fit in nicely within the SLR camera bag. But it still has to be easy to carry around. Since most of the time you will be carrying them around and the SLR camera and its components all together are quite heavy.
There are also SLR camera bags that can carry more than one camera and more than 5 lenses.
You need a smaller SLR camera bag if you are used to taking photos in a quick snap. This type can only accommodate one camera and at least 2 lenses. These bags are also water proof.
If you are the type who goes hiking, fishing, or getting lost in the woods just to take precious shots, then you should look for a SLR camera bag that is terrain and weather proof. There is also a camera bag that sort of works like a belt bag.
When you are carrying more than one SLR camera and at least 10 lenses, then what you need is a big SLR camera bag abundant with compartments. If possible find one that can be adjusted between a shoulder bag or a backpack.
a SLR camera bag should reflect what and where you will use it. This is how you determine what kind of SLR camera bag that suits you just fine.