Source: I've mucked up multiple small engines with bad stored gas.

Propane, sure, but now you're talking about something fairly exotic, at least in terms of vehicles you can buy "off the shelf."

In any case, you can't produce propane yourself. You can "produce" electrons with a solar panel.

But for conversations sake, if we're talking about diesel trucks, and specifically an old mechanical diesel like a 7.3 ford or a 12 valve cummins, and we're talking about stored diesel, ideally a class D died diesel with a high sulfer content, then you'll get considerably more lifetime out of it than the recommended 18-24 months.

Additionally, you can burn about anything, old motor oil, fry oil, diesel with algee in it if you treat it and change your filters. A good, mechanical, not very picky diesel will burn fuel that is 20+ years old. Not forever, and you'll go through some filters and maybe injectors. By the time you get to fuel sources that can't be burned in a machine like that, or you've burned it up past your parts and ability to repair. you'll probably have a lot of other problems.

If we're talking generators, you can get off the shelf propane generators and propane stores well.

If you have a vehicle that runs on gasoline, you don't have to store gasoline for a long time to have a stockpile.

The cost of a few empty canisters is by far smaller than the cost of solar batteries, and putting gas into a vehicle in case of an emergency within a span of seconds rather than hours is a huge asset.

Not to mention: not everyone has space for solar. City dwellers are particularly constrained (as in: people who live in apartment complexes).

Finding space for a solar battery installation is a bit harder.

Not to mention: your Cybertruck isn't going to power your 7th floor apartment. You can probably figure out why.