Scott Pelley on CBS tonight just asked Leon Panetta if Trump was rational. Panetta's response

[Hortensis]

14. "Collective first strike"? No.

We have a stronger military than all the rest put together. They could take out our capital and all our major cities and still lose their nations. They know this.

But cyber or EMP from a high-altitude nuclear weapon are not exactly impossible. Stocking up on a few months of food, as much water as possible/needed, vitamins and medications is only sensible. Paper maps, walking shoes, and water in cars. Arranging means of communications with family in case all electronics are down, etc. Tuning up the old bicycles just in case they could be needed. And then forget about it.