Any suggestions for a backpack (sorry don't like single shoulder sling bags) that could store a D750, 1-2 lens, battery charger, and a few filters but still function as a normal day pack for touristy things? It seems like just about all the camera backpacks I have seen are purely dedicated to being camera bags. So looking for a bag that preferably has a quick side zipper but then room for snacks, maps, water bottles, junk my wife thinks is cute and I need to haul around for the next 8 hours haha.
I have an f-stop backpack that I totally love. I mention it because although I got the biggest insert it could handle, there are smaller ones -- they would leave room for the other stuff you need to haul. It's really well-made.
I got the Loka
https://shop.fstopgear.com/us/products/mountain/backpacks/loka.html
with the Large Pro insert.
An unusual feature is that you get into it from the straps (back) side, not from the outer side. So, true, it's not a bag where somebody can open the main compartment when it's on you. Top (2 compartments), yes, and there's a shallow compartment on the outer back that could take outerwear (but not a lot of it).
With the insert out it could be a good daypack, but there are no compartments in the main compartment, so you'd have to stuff everything in there. It has a dedicated hydration pouch -- anyway, I love it. Fits in an overhead bin well, too. The last time I travelled I had a D810, 70-200 f/2.8, the 105, 14-24, a Marantz field recorder, Sony RX100, batteries, filters, charger, cables, etc etc.
Not cheap, but beautifully built, and with a small insert it might be what you're looking for.