Originally posted by klkitchens: ... keep it casual and really want to use a prime for this, but seems I always panic and fall back on a short telephoto for this kind of thing ... Have a simple belt clip to keep thing unobtrusive as we roam ...
Your thread title says walkaround but some of the things you said make we wonder about what type of photos you have in mind. Do you want to take photos of whatever you happen to come across, or closeup photos of strangers, or slightly wider streetscapes of buildings plus people?
The K-1 body is fairly large so the choice of lens may be secondary to how "unobtrusive" you are. Anticipate that photo subjects, ignorant security guards, and potential camera thieves will sometimes notice your camera.
When I'm doing general "walkaround" photos I like the 28-105 for its versatile zoom range and it's fairly small size (for a zoom).
28mm is still a good focal length for stealthy street photography "shooting from the hip". I pre-focus around 2 meters away, set the aperture to f/8 or f/11 for good depth of field, relatively high shutter speed to freeze motion, use TAv mode to let ISP drift as needed. This can be done with the K-1 but IMO works even better with the tiny Ricoh GR. Going as wide as 28mm often gets clutter within the frame so I crop for composition later.