I will do the following:

Duck and cover

I guess I'd seek shelter 🤷‍♂️

If I’m in a country that isn’t at war, and has a strong military:

Ignore it and go about what I was doing. Later on, probably read about some idiot who sent the warning by accident.

Possibly, die in a fiery explosion.

I assume pizza delivery times will be through the roof, so I'd try to get mine in ASAP.

Get with my kids and hang out... wherever. No basement, so either in a bathroom or get in a car and park it around behind my house and hope it's enough to protect us from the blast. If it doesn't, at least I'll be together with my kids when it happens.

I'm going to the drug store to buy them out of iodine. If I survive, probably going to need it.

Double it and give it to the next person

Nothing I can do. As far as I know there is no bomb safety infrastructure near my house plus I'm afraid of getting trapped underground so I wouldn't want to risk sitting in one.

I'd crack a beer, sit out on my deck and call my family and close friends to say my goodbyes.

Take me and my cat down to the basement with my phone, water, power bank and lantern/candles, call my mom so we could all be on the phone together, and hope I'm taken out instantly.

If I'm at work, I go to the gym (the gym's in a cold war bomb shelter) if I'm at home I start heading north. Put a couple of mountains between me and the city.

I'd either go take a nap, or go hide in my basement. Not sure which.

I'm going to get some beer and weed and enjoy the rest of my day.

Seek immediate shelter, probably. And wonder why someone would send a ballistic missile to New Hampshire.

I'd be setting off the pair of sirens I own, then awaiting the inevitable. Thankfully I live in an area where the chance of being vaporized is quite high.

Get in the cool dirt under my house.

I'd probably be safe and sound, since I'm in a small town a bit away from Melbourne, so an air strike wouldn't affect me unless they tzar bomba the shit out of Melbourne.