Backpacking camera bag

I can't direct you to a specific bag, but have you considered a fanny pack type, reversed so it is in front? I use a reversed fanny pack on my day hikes, it places the bag directly where I can reach it, in front. When I backpacked years ago, I did the same, it didn't interfere with the backpack or my hiking and allowed me instant access to items routinely needed during the day. I prefer that instead of removing the pack to get at items or reaching around awkwardly for access to the sides.

Pretty sure there are small packs to where on the chest and attach to the pack straps too.