A few things I would reccomend based on observation of Hong Kong protesters for the last year.
1. Bring goggles and a respirator
2. Dress in all black
3. Bring black umbrellas (can't count people from above ground, and offers a bit of protection from projectiles)
4. Green laser pointer. Hundreds aimed all of a sudden, popped up from behind the umbrellas would temp blind the police and fukk up police helicopters and drones
5. Leaf blower. Have a few on hand in crowds to minimize the smoke/gas grenades. Sounds odd but just saw a video and fukk me if it didn't nullify the smoke grenade
6. Milk for the eyes if you do get burned by gas