I have a couple of toploaders (in the Lowepro line, you need the Pro versions for a gripped body, I have the 65 and 75). I occasionally wear them on a hip belt, but mostly they're used for transporting a small kit in the car (right now there's the 75 with the 1D X and 100-400L, with the 40/2.8 pancake in the side pocket, leaving for an Audubon sanctuary hike with my daughters in a few minutes).
For ready access, I carry the camera+lens on a Blackrapid strap. Good support, weight is on shoulder not neck, and I can wear it together with a large-ish pack (like a Lowepro Flipside 400 AW, full pack with hip belt, etc.).