Some tips from the EFF (https://ssd.eff.org/en/module/attending-protest).
Before the Protest
- Enable full-disk encryption on your device
- Remove fingerprint unlock and FaceID
- Install Signal
- Back up your data
- Buy a prepaid, disposable phone
- Consider biking or walking to the protest (to avoid Automated License Plate Reader Systems)
During the Protest
- Take photos and videos without unlocking your device
- Enable airplane mode
After the Protest
- Scrub metadata on photos
Personal instance of nitrohorse (nitrohorse.com).