I've thought about really trying to utilize all the stock locations but I kind of hate having stuff squirreled away all over the rig. I really thought about breaking the tabs on the wheel well storage tray things and storing stuff down there, but never committed to it. Now I have 2 rago storage panels, so I don't have a ton of need for it. Still may do it though.
I use the 2 rear cup holders to store 2, 1 liter water bottles that I swap out every few months. I also have a swiss canteen w/ cup in the flatter section of the rear door cup holders. It slides in like a glove with the water bottles.
https://swisslink.com/swiss-canteen-w-cup.html
The only other one I know of that I sort of thought was cool / didn't think of it, was the space under the rear seats. It's just big enough for a strap or something of similar size. Saw someone post about it. I was thinking i could try to find some square zippered pouches that were velcro backed (stick to the carpet) I could throw back there with emergency / survival stuff in them.