LOL at Big White Beast!
But I know where you're coming from-my job as a contract oilfield operator requires me to carry a ton of tools (although I guess technically I could get away with a rock, pair of Vise Grips and a rusty old 18" pipe wrench like some guys do

). A lot of them won't help me much on the truck (if I need a 36" pipe wrench on it I've got more trouble than I can handle on the road

) but a lot will work for either job-digital DVOM, standard and metric wrenches and sockets from 1/4-3/4 drive, screwdrivers, pliers, Vise-Grips, hammers, chisels, hacksaw, Allen wrenches etc. etc. etc. Working on building up my metric selection to handle the truck better as most of the oilfield stuff is SAE-but tools are a writeoff for me so I accumulate as much as I can carry. In fact I had to swap out my Challenger toolboxes for Sealtites to gain more roon-my side boxes were pretty much full to capacity.
As for truck-specific stuff, I always carry at least 4 litres of engine oil and at least 1 spare oil and fuel filter-and extra mixed antifreeze and WWAF. Pretty hard for me to carry a spare BHAF though

. Right now I've got spare ATF+4 (for the transfer case) and the 5600 oil in there from my last change. Also always carry lots of spare diesel fuel conditioner... . I need to add a spare fan belt to my collection-I do have the replacement idler from Gordon at PS running around in there to install so this spring I'll put it on and a new belt-and save the old stuff for spares. Also should add a spare lift pump to my repertoire-that'll happen before I go on any major expeditions. Spare fuses in there somewhere too-should carry some spare bulbs. I do have spare headlight bulbs running around somewhere as well... . Hand cleaner in there too for work as are usually a ton of rags and/or paper towels. And I always have a spare pair of coveralls in case the ones I've got on take one for the team-just because it's a work truck doesn't mean it's gotta get greasy inside! Usually the service manuals are in there too-although right now I have them in the house with me.
Tow strap's a given in the type of country that I work in-as are booster cables. My rig's wired front and back with quick disconnects on a relay-so I can hook up either end, make the connections, and then flip the switch in the cab to energize the works. In the future I also want air-probably gonna put on a wet kit (hydraulics) as I figure I can probably find a use for them too out in the field.
Now all I need is someone smart enough to actually work on it if it breaks down!
Jason