I once wrote an article detailing as many prepper uses for an offline phone as I could think of. Dozens of offline apps useful for a survival situation. My favorite might be ATAK, which is from the US military and allows a team to communicate encrypted over Wi-Fi or radios, completely offline. Share GPS coords, camera feeds, messages, map markers, all kinds of goodness.

And if nothing else, you can always rupture the battery and start a fire :-)