I heard again today someone mentioning Zello as a solution to Internet outages, but it is just not true. Although it appears to operate like a walkie-talkie, it has to connect via the cellphone tower to the Zello Internet service. If either of those are out of action, so is Zello.
Briar is an app for Android and iOS that will allow a number of users in a community to create a mesh network using WiFi or Bluetooth, and in this way you can text chat to someone out of range of your phone, as long as there are Briar users at hops in between you. But you want to have it installed now, and ensure others in your community also have it installed, or you cannot connect.
Failing that a good pair of two-way radios is also not a bad idea as those are standard channels across different brands of radio which means if just a few folks in your nearby community have radios, you are able to communicate up to 800 m or so apart.
Of course ham radio is a lot better reaching up to 10,000 km or more, but then you need a license and the equipment can be a bit pricier. There are cheaper VHF portables though that will also work well, but again you need a license to operate it (unless it is an emergency and there is imminent risk of loss of life).
The Zello walkie-talked cellphone app is certainly useful in an emergency situation, but it still requires either WiFi or an LTE network connection to function.