We don't know how this works, but it does. Use a mild one to avoid irritation. Water High temperatures and frenzied activity lead to heatstroke and dehydration. When in doubt, drink up. Water's also good for flushing chemicals out of your eyes and cleaning out wounds.
Eyedrops Bring 'em to combat pepper spray, tear gas, and fatigue.
Carbohydrates Keep your energy up with granola bars or other snacks that keep well in the heat. Fruits are fine if they're not too squishy or juicy. If you're planning anything confrontational, you'll want a mask to obscure your identity. Since you never know what'll happen, it's a good idea to bring plastic.