Funny this should pop up, I've been researching bags for what seems like the last two weeks. (I can find everything but the one I want!) Anyway, there are a staggering array of bags made, and in this age of compact and mirrorless digi-cams, a whole additional continuum of smaller bags appears to exist. (I'm actually looking for a fairly compact one for a modest Canon EOS M5 mirrorless system at the moment.) Many newer bags will have little pockets for memory cards but a film shooter could use those for sticks of chewing gum or change for parking meters.

There are all sorts of holsters, slings, belt pouches, waist packs ...
At any rate, Domke, Lowepro, Tamrac, and Think Tank all make a slew of relatively high quality bags. Many offer one or more padded velcro-attached dividers that can subdivide a space -- or cradle a camera with lens hanging down. The problem is to determine what "features" you do or don't want and how big you want it to be. And there are many other makers. My current bag for the EOS M5 is a sort of fat holster from Ruggard with a separate pocket on the front which appears to be reasonably well made, just not able to handle an extra lens of any size and a few other trinkets I hope to include.
The four makers I mentioned have some varied designs that they offer in a series of two, three, even four sizes. The B&H website is pretty good about listing interior and exterior dimensions of the main compartments. I tend to arrange what I hope to put in the bag in likely configurations and try to measure. (But I haven't clicked 'Buy' yet!)
(I think I may have more bags than cameras -- seems I get a new one for every major trip.

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