So that native guide may have a sat phone with GPS, and check the
satellite network for the weather that's approaching over the next
few days.

Yes, I had fun with my players - lost in a desert - encountering some nomadic tribesmen. They just *assumed* and were surprised when one got out a mobile/cell phone. Of course, not to cut the adventure short I had them as a couple of disorganized wotsits who are getting the phone out of the bottom of one of their barrows, brushing the sand off it and then finding it needs charging and the gear's back at the camp they're heading to...

But at several junctures the refrain "we're not barbarians, you know" could be heard in response to surprise they had showers in their tents or whatever.

So without huge changes in culture (though you would get them
eventually) you can have some major surprises for characters from
higher TL worlds who don't stop to think things thru (ie a large
percentage of PCs).

So basicaly you can take a "historical" (or fictional) TL X culture
and throw in various higher TL items. Some are luxuries the rich &
powerful importeed. Others are cpommodities that are fairly cheap to
support and useful enough to put up with the limits of having to
import them and difficulty of getting them repaired locally.

GURPS Alternate Worlds sort of does this with its TL+ scheme of stating the TL at the split but then allowing it to develop beyond. I stand to be corrected as I don't know the system well, but found the parallel earth books interesting.

Check out any third world nation, especially in the back country, to
see how this is playing out on earth.

This means you can have a lot of local culture/flavor, as well as
surprises.

and referees do like surprising players!