Icon base by Lorc under CC BY 3.0 with modifications to add a gradient
Now is the time to look into Meshtastic or Meshcore.
The devices are pretty cheap, and the more poeple have it ready when needed, the better.
Also, stock up on guides from the anarchist library. Having an offline copy so you don't have to search for it later will help with going under the radar.
What is it?
Both are mesh networks, with slight differences. The idea is that volunteers run relay nodes with LORA (which has a range od a few KM, depending on visibility), and you also have client devices, and if you have a large local community of enough nodes and users, you can have an off-grid communication network where data is being sent node to node (both client and relay) before it finds the recipient. Both networks are encrypted.
Most cities already have a pretty good coverage. Meshtastic has a few issues that Meshcore tries to solve, mostly in regards to scaling, but tbh I havent researched it enough to be able to correctly list them (just like this answer is mostly a simplification). There's plenty of blog posts that explain it a lot better.
You can get standalone Meshcore devices (with a screen and keyboard) for around 70$, and devices that connct to your phone through bluetooth and you send messages through the network from an app for even cheaper.
My guess is that it's not entirely adversary-proof, but it probably beats having a phone with you to communicate when you're doing anti-goverment sruff.
And if you're asking about Anarchist Library, there's this site that has a lot of articles, zines and books about good operational security, how to behave on protests, what to (not) bring, first aid against common crowd control, and general anti-goverment guirrella stuff so you can protest as safely as possible.
I know certain people in the US are probably clamoring to get their hands on this.