Gas mask I would rate very low on the equipment list but....

I would recommend having a basic N95 respirator mask from 3M in at least your car kit and possibly your EDC if you carry a backpack or Maxpedition.

I have one in each BOB, in case I deal with high dust and airborne particulates. I have actually used one in a monsoon dust storm, but a buff headwear or bandanna would just as good most likely.