I've tried so many bag variations that it's ridiculous. News photographers usually carry their stuff in unpadded or very lightly padded Domke bags, just because of the weight problem -- they carry all kinds of crap around with them, and they don't need a heavy bag to add to the load. Problem with Domkes is that they scream "photographer," and also the load rides very heavily on one shoulder. I've seen the single strap across-the-chest systems, but never tried one. They were a fad for a while with college students, for book bags, but faded (I haven't noticed them for a while; maybe they're still popular elsewhere.) I think the reason that they faded might be that they're less adaptable than a regular book-bag/backpack, which can easily be slung off either shoulder, or both, without even thinking about it. I have seen small "amateur" photo backpacks that would just about carry what you're talking about, and also have some padding. But...you might think about making your own system. Somebody, maybe Domke, makes camera wraps, which are light foam wrappers with Velcro at the corners. You wrap your cameras, lenses, etc., to give them protection. Then you could just stick them in a regular book-bag type backpack; it'd be cheap, discreet and handy, and there are so many good backpacks that you could get exactly the size that you want. Some time ago I bought a belt system, which I wound up not using as a belt, but I use the lens pouches and just lay the lenses on the seat of my car when I'm travelling. I can get at them quickly -- even change lenses while I'm driving -- and they're protected. You could probably use the same pouches to protect the gear when you stick them inside a backpack. One problem with a sling-type bag is the tripod; if you get a mountain daypack, they usually have ties for ice axes that you can use to tie-on the tripod. (I don't like to do that because the tripod usually sits too far outboard, or bangs against your back or your arms, but it is a solution.) When I'm shooting, I don't like to attact attention. If that doesn't bother you, you could always get a tiny pack -- even a fanny pack -- for one the lens, and just carry the camera slung. You can also get a sling for a tripod, and carry that slung, and just skip a big pack altogether.
Something else to consider, before I quit this -- go to a hunting-fishing store and look at the "soft" tackle bags. Some of them would be very adaptable to cameras, and lots of them are waterproof or at least more water resistent than camera bags. Tool bags from a good hardware store are another possibility.
I oughta be a bag manufacturer. I find them kind of fascinating.