Outfitting a new-to-me pickup truck, I got one of those 'seatback organizers' that is set up for attaching small packs and pouches via mollie straps and/or velcro. So, a med/trauma kit is there, a few different meds, spare loaded mags for the G19 that's always in the truck, a couple of different knives, multi-tool, zip-ties, paracord, binoculars.
In underseat storage I have a plastic ammo can with a variety of ammo for whatever I may need on most given days - .22, 9mm, 10mm, .45, 5.56.
The mounted toolbox has all sorts of recovery gear, tow straps, gloves, camping blanket, MRE's, Sterno stove, inflator, tools, machete, crosscut saw, tarp, etc. Not as neatly organized, but I kinda know where everything is.