The Red Cross has some helpful suggestions about what to do and what to have on hand. I didn’t know that you weren’t supposed to go to the basement because many chemicals/gases that could be used are heavier than air and if they get into your house would settle in the basement.
I have most of the stuff for a kit (just not all in one place), but it looks like I’d need more duct tape and some visqueen and I should stock more water. The MIL lives 70 miles away, upwind from the big city, so we’d probably want to get there if possible if there was some sort of bio/chem attack in our area.
Feel free to loot my house; just be careful of the two booby-trap shotguns I’ll have set at the most likely entry points. Just kidding (maybe).