Sorry it took so long to reply for the parts thing
I did my trip Charleston, SC to Seattle, WA, wheeled in KS and in Moab, this is what I consider critical parts:
At least one CV joint
A pair of tie rods (probably weakest link in front end other than CV joint)
I don't carry, but would consider a center drag link, especially if you do HD tie rods
Rear Drive shaft
A front prop shaft would be nice, but not required, you can almost always get out in 2LOW if you have to (I carry both shafts)
Fuel pump
Alternator
Serpentine belts
Fuses
Tools of course
All types of fluids
Hose patch kit
Lock wire and pliers
AC inverter
Extra drive flange or manual hub, I assume you will run manual hubs for better MPG and reliability and if you bust one CV, you can prevent TOD from throwing a fit.
Metric bolt assortment, like a kit from a parts store, has all kinds of sizes.
Large zipties, 100mph tape, JB weld or equivalent
Printed copy of shop manual or even an electric on your phone/tablet/laptop would be a good idea as well.

Short of an engine failure or tranny/transfer case failure, the above things will ensure you can get back to civilization. You have to be able to steer. The engine has to have fuel, electrical power, cooling and you have to be able to spin the rear wheels, everything else is just luxury...lol.

I also bring a welder, grinder, impact, CO2 bottle (or nice compressor) but those stay at base camp due to weight and size. This is why I like the trailer idea, if truck has problems, you can always dump the trailer and tow truck out if needed.