The chemical agent is solid at room temperature and its the heat from the canister that makes the gas. It has been said that putting the canister in a bucket of water will cool it down and stop the gas from coming out. I have never had the chance to test this but its worth a try. Also bring insulated welders gloves or something to pick up the canisters with. The canisters are really hot and will burn your hand without protection. Large sling shots are good for getting the canisters deep back over the police line.
Protection from gas:
Gas masks are best but if you cannot find or afford one try these alternatives:
Soak a bandana in vinegar put in zip lock bag. Double bag it to avoid leaks.
When gas is fired remove bandana from bag, Place over mouth and nose and get out of the cloud. If you cannot deal with the vinegar some have said coke cola helps.
Get swimmers goggles or something to protect your eyes. The gas gets into your clothes too, so bring a poncho and close openings with large rubber bands.
Also there is this from wikipedia: washing with an alkaline solution of water and 5% sodium bisulfite. Never tried this not sure what sodium bisulfite is.
For the rubber bullets bring shields and or body armor or make your signs out of some hard.
Remember don't scatter stay together and protect each other in a nonviolent manner. If you need to pull back do so as a group.
If you do get broken up have a rally point selected in advance to regroup and resume the protest.
Have some people in reserve to do un-arrests if possible.
Hope this helps