Depends. I have a nice lowepro DSLR sling, but its very specialized for the camera. I've repurposed normal shoulder/messenger bags for my camera to fit a theme (Dapper Day), and I've used a backpack to just toss it in, as well as just doing the camera hanging off my neck. They all work.
One thing I've found is that even when I bring a second lens, I never swap the lens. Just added weight to be dragging around. I've got my setup tuned to the point that one body, one lens is all I need for how I shoot. That could change if I get the next lens I want though because they are so different on the focal-length. I only shoot prime in the park, so my zooms go unused 99% of the time.