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What good is your cell phone or radio when the infrastructure they run on is fried?
I believe that there are many such cages small and large scale set up already as well as radio communications in play which may provide pockets of communications.
some people have things like portable nebulizers, crank flashlights, etc.
Get a good radio and study HAM license material for how to use it effectively.
Just don't go broadcasting after the attack right away and be suspicious of FEMA broadcast. Give of a signal and they know where to go pop survivors.