Most apps will run and if the data is stored on the phone will work correctly if they can get a GPS fix.

Google maps goes to the internet for its maps by default, but you can download a block if you need to.

I use Back Country Navigator when hiking. You select the area you want to download while you are home and then those maps are available while you are out of cell coverage area.

MAPS.ME is the same thing, only for road maps. You can download state maps with routing info.

Best thing to do is turn off the cellular data and make sure it does what you want before you go to the boonies.