WRT "gas masks". Look at modern masks from major companies. Try Googling "silicone half mask" for example. You can get a wide variety of cartridges (research what each is good for) and the silicone material is soft, long lasting and inert. Learn to clean it, check for proper fit (good ones come in sizes). Half masks are small and light.

Note these can also be used for dust only with the proper filters.

N95 is better than nothing but it is woth getting N100 / HEPA IMO.

Get some practice cartidges and get comfortable with your equipment and leave your actual emergency cartidges sealed.

Wheels are a great idea IMO. I purchased a fold-up cart that I leave in my work area as well as one in the trunk of my car.

I work in a downtown office in Seattle and leave a large duffle under my desk with supplemental goods (I have a EDC bag that is my primary), including a pry-bar, hacksaw, etc. I also keep extra first aid and flashlights for my co-workers. Basically, tools aside, I've set aside items for others to avoid depleating my own supplies.

I also have several cases of bottled water in my cube area.

-john