The Black Cross Health Collective in Portland, Oregon has produced a manual for demonstrators and activists on basic first aid and treatment techniques for tear gas and pepper spray. The manual also has great field-tested info on what to bring/wear/do to maximize your ability to withstand pepper spray and/or tear gas.
Black Cross has created a 'zine with the above info and put it up on their website for general use, downloading, printing, etc.
The Black Cross Website is at : http://www.blackcrosscollective.org/
Info on demo preparation is at: http://www.blackcrosscollective.org/beprepared.html
Info on tear gas/pepper spray starts at: http://www.blackcrosscollective.org/chemweapons.html
The downoladable 'zine (and other great info) is at:
http://www.blackcrosscollective.org/downloads.html
Good luck!
Kirk