If you are in an area where fallout is an imminent danger to life sitting in a hole eating canned beans won't do you a bit of good. Get in your car and leave the area. You will be long dead and rotted up in your hideyhole before the environment is safe.
The decision to stay or go has to be made where you are and how prepared you are. 8 days after fallout begins, you will be safe to "get in your car and leave the area" if you have planned well.
As soon as a launch has been confirmed (for sure sies, remember Hawaii's launch scare?) is a good time to distribute doses of potassium iodide and start intake/uptake.
Some will be able to leave, some will be in error to leave and die in traffic and gridlock. Once you start to run from fallout, you are committed regardless of traffic, roads, social unrest, etc.
Not saying it is the wrong decision, it just has to be made with care and thought as early as possible. Plus, your route(s) and destinations possibilities need to be planned.
Fallout has a half life, it loses half its energy every 24hrs. Acceptable levels are achieved on day 7, day 8 is even better. True the environment will not be habitable, but you will leave with more than you would have if had left on day 1. Roads will be clear(er) on day 8 as well. Water is not affected by gamma passing through it. Water in sealed containers will still be drinkable.
I think the big deal will be looting zombies (I say that with some half truth) and those caught in the open looking for care, food, water, shelter, etc.. A dedicated suit and a defense kit outside (hidden of course) is helpful for making contact. Moving a defense kit in and out of your hideyhole is not really doable without a proper wash room.
A safer way to make contact is via radio. hang a cheap radio (say a baofeng bf888) on a fence, wall, door etc. and a sign to turn on radio and Tx to make contact. Much better than a face to face in the situation. Maybe hide some bottles of water and/or food nearby to direct them to if you think that is a good choice, The radio gives you an opportunity to read them better before you offer any help, care, etc..
Solar. Assuming it was not a EMP and your backup solar is operational, you will need a way to keep the panels dust free. Obviously, sweeping fallout dust is a bad idea. A remotely operated fan system would be better, even if it only worked a short time. Think 8 days. As I understand it, a disconnected solar panel will survive an EMP, it is the other parts of your system that will not, like the BMC on lifep0 batts and the PWM or MPPT controller between the panel and batts. Keep as much stuff as possible close to you, meaning, put the batts, regulators, etc in a area that you can work on it without risking exposure.
MAKE sure your NBC filters are not expired too. You can go a year or two out of date but the degrading filter will shorten the usable life.