Have a front over the wheel rack then you have a place to attach a camera bag,..
Klick fix can use a rear mount seat post and put handle bar bags back there .
[their panel clip could be fitted to a Pelican Dry Case]

Back in the Film era I got a Lowe Pro Photo Fanny Pack, It stows waterproof in a Small Ortlieb rack pack,
and if you have a wide Porteur type rack , You can put a pretty good sized Bag into that large rack
and grab it when you park the bike.