What if you don't have a trunk?
I have:

In the glove box:
owners manual, manual for cb radio.
tire pressure gauge.
trailer plug adapter.

Under drivers seat:
GHB, camp ax, droid mount (when I don't have it on the window.

Under passenger seat:
FAK

Under rear seat:
Bag with jumper cables, spare lug nuts, spare bulbs, S hooks, misc other small parts.
Tool roll with socket set, fuel/trans/ac coupling tools, screwdrivers, mini hacksaw, etc
Wrench roll with wrenches and long 1/2" breaker bar.
pipe that fits over the breaker bar or factory lug wrench
Factory jack
Zipper binder with various maps
Ziper binder with schematics, etc
diaper bag
toddler potty seat
chain
12v air compressor

Front door pocket:
Unbrella, suglasses, bible.

Underhood:
Second battery, isolator, extra fuse block with high amp fuses for branch fuses, trailer power re-routed to second battery. fender mount CB antenna.

Mounted in cab:
CB radio,
fuse block powered from second battery
extra 12v ports from fuse block
hardwired USB power port