In the book “One Second After” (which I found compelling) about 90% of the population dies. Those who survive strikes on the cities will start roaming the suburbs, then countryside. If you don’t have guns/ammo, you will not survive very long.
After the first 4 months, food stores may be exhausted and radiation may make any food that is grown inedible.
I would not be surprised if only 5% of the population remained after 2 years. And the survivors would have it very rough indeed.
Don’t look for any of our neighbors/allies to come to our rescue.
“Radiation” doesn’t make food inedible.
Fallout can be rinsed off. Don’t eat the fallout.