I most often use the
Lowepro Passport Sling which is a simple over-the-shoulder bag. It's not too large for daily or incidental use and comfortable to wear for long walks.
Although it is made for a body with mounted lens and perhaps one additional lens, I find that it can carry much more. The rear has a zipper that expands the capacity. Using something like a
Tenba camera/lens wrap or
Domke protective wrap (padded cloth with velcro), more items can be placed in the non-padded rear. The wraps come in different colors so you instantly know what's inside each one. For extra padding in the rear, I usually add an additional open wrap on the bottom/sides, then load the wrapped lens or body.
In the front compartments, I can carry more than one prime per compartment. Again, the wraps are used to cushion and protect each additional lens, stacked in the bag's thickly padded area. If I carry the camera over the shoulder (
sling strap) or with the
Peak shoulder strap, the bag can carry a half dozen lenses.
(I do use
safety tethers, just in case anything fails on the camera attachment).
I've carried both my K-3II and K-5SII bodies in the bag, with another couple lenses besides those mounted. There's space for a water bottle in front. Small pockets for a notepad or other items. Zippered inside pocket for batteries and memory cards.
It's not too much, not too little, and flexible for small or larger loads.
The Passport Sling is now into version III. I have one of the originals and one of version II. I prefer the original. Seems like they got that one right and the other "improvements" weren't really necessary. ;-)