GPS receiver are passive device, they do not transmit your position. However, we’ve seen in Ukraine and middle-east that GPS are easy to jam.

As other have stated ham radio are simple to build, long range, and reliable. However, once you emmit it’s fairly easy to pinpoint your position

I am not sure why Local peer to peer network haven’t been a thing. i am old enough to remember the era where we had network cable hanging from the windows of student residency to build a kind of building-wide LAN, looks so much easier with wifi

Be careful with encrypted mobile phones, The Enro-chat network let the police listen to drug-lord in clear for like 2 years leading to a massive arrest. I believe it requewstd a huge work for the police to arrest them, but they’ve done-it Encryption may still help though, just don’t over estimate the budget government can put to break-it if needed (let alone all the backdoors in commercial-grade devices).

Pigeon, dead-drop, and courrier are very efficient, it doesn’t look as cool as space hacker. but this works