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Groups and organization
You can use a Telegram Channel to keep updates of the demonstration (as they did on HK), if you chose to use a smartphone. In the information include: time/date/context and maybe a picture. If you take pictures, make sure no one's face (or other significant recognizable detail, such as a tattoo) appears without consent. Offer stickers with 'No pictures please' message on them if you can afford that. Spread the Channel link or name.
Communication
If you go in groups, try using a radio transmitter/receiver to communicate with a partner, instead mobile phone. If you speak sensitive information then use encrypted messages, for his take a look at Jitsi. Also consider start using Riot.