I'm seeing a lot of people talking about Zello and other apps as backup communication during a disaster. Specifically how well this worked in Houston during Harvey. There's an important distinction to be made here.
In Houston, much of the communication infrastructure was still operable. Power stayed on to the cell towers and they still had connectivity. [1/5]
The problem there was that the telephony network was saturated. That network is designed around the notion that you get a guaranteed circuit, even if virtual, for that call. Put another way, if you place a call, it either goes through or it doesn't. There's no middle ground.
Internet connectivity is "best effort". That is to say, each router will fling your packet in the appropriate direction and hope for the best. [2/5]
I recommend getting some FRS radios. These will cover a small neighborhood (about a mile across) fairly reliably. This is useful for coordinating activities like movement of elderly or other special needs folks to houses that still have power and cooling. You may also wish to consider getting your amateur (ham) radio license for extended range communication of health and welfare information. [4/5]
It's probably also worth noting you can't just go out and get an amateur or GMRS license and the supporting gear. That would require some advance planning. FRS radios are usually in stock at your local big-box retailer though. [5/5]