The main issue is that I like bags, so every now and then I need to resist getting another. But for now I have these solutions:
1) every day, it's a think tank perception 15, it's "daypack" with room for food and clothes, camera gear, and a laptop, I use it for my commute. This works well for me because the focus is on getting to the camera fast, while still having room for daily stuff, so I can reach to the camera quickly when I need it.
2) Hiking with an insert bag (tenba byob 9, fits the k3ii and 2-3 lenses). the same insert fist in my bicycle handlebar bag for overnight tours and day trips. By far I'd rather have a purpose-designed backpack with a frame and suspension system, plus all gear attachments for winter hiking, because those have to work and camera gear is just my fancy.
3) Around the city with a small shoulder bag, fits 1 zoom or 2-3 small primes and the camera. Nothing special, just compact and unobtrusive when going out or to a concert.
4) Ricoh GR camera in a small pouch, works in winter coat pockets or any other bag