Communication means staying connecting and being able to ask for help.
Zello: Is a push-to-talk app that you can download to your smartphone or tablet and connect to other users or form a group. The cool thing is it only uses data to send the message to the cloud. So even if cell towers are clogged, your phone will keep trying to send the recording with data until it gets through, so it doesn't need a steady connection to send someone a message as a call does. Then people monitoring the channel can see it and reply to it if needed.
Power: Walky-talkies and other point-to-point devices are great if you have a way to keep them powered. Below I have a BeoFend radio and battery than can be charged by a USB adapter and works with your car or solar charger, along with other options.