What to take

^^^^^^^^^^
I agree with old guy.

K.I.S.S.

You don't state how you plan to spend the evenings. Boon docking or in an RV campground? BLM or partial/full hookup? Other?

I find it helpful to have a wide range of saws for the unexpected tree trimming that may be necessary when allowed. A hand saw, a chainsaw, an electric recip saw, and, a skillsaw have often come in quite handy. Often, with a few minutes work, I've made a campsite that others consider "unusable" into a perfect site. Next year when I come back, others now think so too!

Chum lee

It's funny, I used to carry spare parts (alternator, belts, hoses...etc) and once in awhile would need them. I stopped carrying spare parts about 10 years ago and haven't needed anything. Same thing happened with roadside assistance I could have used it when I didn't have it but once I got it I've never needed it.

I didn't see you mention anything about a small bottle jack. That takes virtually no room at all and can be used on the truck and camper. Also, I recommend taking 1 or 2 light duty (14GA) extension cords, 25-50 feet each.

One other thing (and I might get laughed at here), but I assume your hybrid trailer is a single axle and very light weight...so carry some HEAVY DUTY zip ties. You might be surprised to know that, if you had a leaf spring/axle u-bolt break, you could actually provide enough TEMPORARY support with 4 of these zip ties in place of the u-bolt...enough to let you limp to the nearest exit/rest area.

Generally speaking, I think there's really no limit to the amount of small things you could carry along. If you have a small tool box that you take anyway, just make it sure its 100% full to the brim of anything you could think of. In other words, if you have a 10x20 box, it takes up the same amount of space if its empty or full.

As long as you've got a couple credit cards, a cell phone, and a little cash, you're good.

I traveled many years through the area on a motorcycle, and didn't have room for much more than that, no cell phone of course. :) And never had a serious issue. Like has been mentioned it's not the "Old West" any more.

it sounds to me like you've got things pretty well covered. I'm assuming the hand tools include a #2 Robertson screwdriver, without which it is nearly impossible to fix anything on an RV.

If you don't have a set of warning triangles, they would be a great thing to carry along should you need to stop alongside the road for whatever emergency; likewise a high-visibility vest. (In dry areas of the west, the triangles are much preferred to flares in as much as triangles aren't known to start wildfires accidentally.)

I would inspect the truck and trailer before leaving, and do any PM that might come due while I was gone.

I would leave 1 generator at home. You're leaving in September, which can be a very hot month once you get to AZ,NV,CA. Unless you think you will be that far by October, you won't need air conditioning. Other than A/C, why would you need 2 gen?

I don't carry spares of anything. I long ago stopped playing that game where you try to guess what is going to fail, and then it is always something else that fails. Then next time you buy that thing, and it will be something completely different that fails. Soon you are carrying way too much stuff and suffering stress related heart failure. I make exceptions if something has a pattern of failing often, but only if failure of that item would be a major issue that I couldn't live without.

Don't over think it.
You're not crossing the open desert in a covered wagon.

Just keep in mind that "out west" is no longer wild and uncivilized. We do have lots and lots of basic services and stores out here now. You can find a Walmart, Home Depot and a Starbucks at most any town along the way.
We travel light and deal with what comes up when it comes up.

No need to pack along enough tools and spare parts to completely refit an nuclear submarine.

Have a good trip.