One of the things I hate most about modern phones is that so few of them let you, the user, change out the batteries. In the days before this norm, I always kept two spare batteries in my evacuation bag.

Now, things have changed a bit. I recommend keeping not only a battery pack but also a hand-crank radio that has a powered USB as well. This will let you, as I had to during Irma, crank your phone to charge it as though it were some odd mix of a phonograph and a smartphone.