Size the bag with the lens attached
Lay out the camera as you expect to carry it, including the lens, strap and any small accessories. Measure that arrangement and test it in the bag. A tight fit that requires removing the lens every time can become inconvenient on the street, while a much larger compartment allows the camera to shift unless properly divided.
Keep spare batteries and cards in clearly defined places. Protect battery terminals according to the manufacturer's instructions and applicable transport rules. Avoid letting loose keys or coins share the equipment compartment. The goal is simple access and separation, not a maze of pockets that makes it hard to know what is missing.
Compare a dedicated bag with an insert
A dedicated shoulder bag can make a small camera easy to reach, but the weight sits mainly on one side. A padded insert in an existing backpack may distribute the load more comfortably and leave space for a jacket. It may also require taking the backpack off whenever you want the camera.
Try both approaches with the same equipment. Walk, sit down and retrieve the camera in a safe setting. Check that the opening stays manageable when the bag is on your lap or held in front of you. A quick-access panel is only helpful if it does not make the rest of your belongings difficult to secure.
Leave room for ordinary travel needs
A bag perfectly fitted to camera gear can still be wrong for a day out if it has nowhere for water or an extra layer. Keep liquids separated from the equipment and do not assume a bottle pocket cannot leak into adjacent fabric. Consider whether carrying a second bag would become cumbersome on transit.
Check official bag restrictions for museums or attractions on the itinerary. Some locations require storage or limit larger bags, and camera allowances can be separate from luggage allowances. Pack the smallest kit that meets your photographic purpose. A familiar lens and a comfortable bag are often more useful during a long walking day than several lenses carried mainly because the compartments are available.
