A couple of "fishing trawler" launched nukes from our coasts detonated a couple hundred miles in and up will make it all moot.
I judge this a very small probability. But it is totally doable. And it would wipe out electricity and all electrical devices in the US. No pumps. No cars. No tractors. No trains. No water system. No waste system. No transportation. Your travel radius is now what you can walk (or bike if you have one, or ride if you have a horse) in a day. Farming would be restricted to what you can do by hand and horse, which isn't most farms. It would take a year to get things going, because you'd have to string new electrical lines, get new huge transformers, new generators, new motors, new cars, new pumps, etc. Other nations wouldn't be able to get enough food and water into the US. Roads would be clogged with dead cars. You are talking a need like the Berlin Airlift x10,000 x356 days. 90% of Americans would die. Ones in areas without access to water would die in a week or two. The rest from starvation later.
Unlikely, but with dire consequences. (i.e., (probability) * (magnitude of result) is not infinitesimal.) So, I looked into what it would take to survive such a thing and found it was pretty cheap and easy to do.
A 5-gal bucket of beans (if sealed with oxygen absorber in mylar bag) will last 30+ years. Same for a 5-gal bucket of rice. Rice+beans makes a complete protein, so you can live off it for a long time. (Wouldn't like it, but could do so.) One 5-gal bucket is about one man-month of calories. It costs about $20 to make one, and about 10 minutes of work. Do it once. Set for life.
So, do that to get whatever amount you want. I did about 0.5 to 1 year worth for my family.
Also added a filter so I could get drinkable water out of ditch water. Some guns. A bucket of salt. Gives me and my family a chance at living through such a thing in the unlikely event it happened.
Also put a backpack in my car and wife's car with enough stuff in it to travel on foot several days. (Some water, food bars, knife, lighter, mylar poncho, rope, cash, flashlight, compass, etc.)