Not popular, but suicide is an option if you can see the bomb's impact close enough that you know you will either be hit by a heat wave, fallout, or scavengers after the fact.
International Level: Specialist / Political Participation: 39 3.9%
Personally, if I knew there is going to be a bombing beforehand, I would've built a fallout shelter to hide in or bought an airplane ticket out of the city. But, if it's immediate, I would run into the attic and hope for the best.
First, if the bomb is within the vicinity (Around 15 miles away) and you don't have time to go away, run into a stable building. After initial impact, then take off all clothes and then take a shower to remove the radioactive particles clinging to your skin and clothes. Wear white if possible to increase the reflection of radioactive rays.
Would it even be worth living after something like that? If you are near the bomb site you are gone. If you are a few mile off you are burned and if you are further off you will sub come to a damaged economy with no infrastructure. Possibly mass panic, looting and lawlessness. I hope the bomb falls on my head instead.
International Level: Politics 101 / Political Participation: 8 0.8%