I carry quite a bit of stuff.but probably not as much "survival" things as I should,especially in winter..I have enough tools to do most minor roadside repairs like change a belt,alternator,fuel pump,starter,etc,and carry some spares of those items if I have any--I try to carry an electric fuel pump too--also have an extra set of locking hubs,and most of the fluids I'd need like oil,P/S and trans fluid,coolant,etc..and an empty gallon jug and 5 gallon pail,those can save your butt if you need water from a swamp to refill a radiator..pieces of rubber fuel line of all sizes and clamps,to patch up a popped tranny cooler line ,etc...
I want to get a full sized floor jack and one of those 12V or cordless impacts to change flats with..its bad enough wrestling a 120 lb, tire and 8 lug rim out of the bed (I'd never mount the spare under the truck in the factory carrier,screw that!)...never mind having to unscrew 8 lugs that come off stiff every last thread most of the time,and almost getting killed trying to jack it up with the stock jack,or a bottle jack.,while semi's blow by you inches away at 70 mph!...getting too old for that crap!..
The biggest problem in a single cab pickup,is where to put all this stuff..I have a toolbox in the bed stuffed with most of this stuff,behind the seat is several lengths of chains,a small 12V winch,ratchet straps,more tools,spare belts,and the front floor on the passenger always has a box of extra oil,filters,come-a-long,and snow brushes,etc..so having a passenger ride with me,is usually not possible...
I could litteraly fill a trailer with spares like a tranny,steering box,and other "stuff"..
I have considered mounting some ammo boxes I have on the stepside bed between the cab and fenders,also thought of mounting the spare tire there,so it wont be buried under cargo in the bed next time I get a flat..(like 10 minutes after loading the bed with a few dozen pallets for firewood,then have to remove every last one to get to the spare!)

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I have also considered just taking off the old stepside bed thats getting pretty shabby and putting my 8' flat bed on it that I kept off my last GMC,that has an electric crane setup on it--and put those ammo boxes under the flat bed..but that'll need a new floor and paint,and I am torn whether the truck is worth that kind of labor now..
I could put a "box truck" body on my truck (I have 12' one I use as a shed..)--and fill it with all this stuff..they suck for visibility though..top heavy..not worth the effort !..
I liked my van,you could toss a lot of stuff in that thing,and still have room for humans and survival gear...here having a "zero-zone" coveralls and some extra jackets and blankets with you in winter,could make the difference between living and dying,in a blizzard scenario..after seeing how vicious it can snow here last year,I respect Mother Nature a lot more than I ever did previously...
Having some non perishable food,crackers and water with you isn't a bad idea either...I carried a propane camping stove and propane in my van at all times...its nice to be able to make hot soup if you get stranded--try that in a pickup truck!..more than once I broke down in my plow truck (or got it stuck !) .while doing a customers parking lot,and had a long wait before a friend could come help me out..