I'm assembling a small kit for a non work truck. Here's my list so far.
Fuses
Large & small phillips head screwdrivers
Large & small flat head screwdrivers
Needle nose pliers
Side cutter pliers
Adjustable pliers
Vice Grips
Crescent wrench
Hammer
Zip ties
Duct tape
Jumper cables
Electrical tape
Knife
Flashlight & extra batteries
I'm often out where it is a LONG walk back if the truck won't run.
In addition to what you have:
Haynes manual
Multi Meter
OBDII Code Reader
Heavy duty zip ties (the type used for HVAC ductwork)
Set of wrenches
Several sets of vice grips
Long nose
Diagonals
Leatherman
Socket set w/ universal, 3/8 to 1/2 adapter, various extensions
1/2" sockets
1/2" breaker bar
Allen set
Hacksaw
Propane torch and bottle
Air compressor
Tire repair kit
few short lengths of all thread
Hi Lift Jack
Large (enormous) screwdrivers x 2 (for taking tires off rims, pry bars, etc).
10' length of 12 ga. stranded wire
Small Axe
Small shovel
BFH
Tow strap
50' extra synthetic winch line
Safety glasses
Leather gloves
All of that, plus a spare starter and 3 qts water fit in my UWS slimline crossover bed box (not a big box. Only about 12" wide).
Additionally when in the boonies, a small chainsaw is always in the truck.
Spare lower control arm and upper control arm ball joints and steering rack joints under driver's seat.
Spare timing belt, jumper cables, and various recovery gear behind back seat.
Battery pack under passenger seat.
A lot of this stuff has saved me a long walk (or a good amount of time missed in the field) more than once.
Have held a broken trailer leaf spring back together with 4 vice grips, well enough to finish getting to camp and back out over rough roads.
Big zip ties (x4) just used last weekend to hold a freshly broken motor mount together well enough to climb out of a rough canyon in low range. Without them the fan was hitting fan shroud when on the gas, and could not get out of where I was at for fear of seriously breakin' chit. Saved me an 8 mile walk back to camp.
Have charged a nearly dead battery with 9 D cell batteries taped end to end and wired up to the battery terminals, well enough for the truck to start. All I had at the time. Now I keep that small battery pack under the passenger seat.
Sounds like a lot o' chit, but it doesn't take up much more space than the tool box, and unused space in the cab of the truck.