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.
International Level: Politics 101 / Political Participation: 2 0.2%
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.
International Level: New Activist / Political Participation: 12 1.2%