I use the patagonia double haul which is not as good as the one I envision in my brain but it's pretty good for reality. It's a sling style with a very good front compartment albeit easy to over load because of it's multi-layered compartments. but that's my fault not theirs.
The back holds a water bladder, light rain jacket and lunch. The sling has to be properly adjusted for your build or it does not stay put well, once adusted it's fine - night and day.
It was yet another lost item in my drybox at boneclave