Full length on youtube, called Threads. About a general all out war, from a UK perspective, and what could be expected as per survival in the aftermath. I guess..something like a big CME or EMP burst taking down the grid would have similar, but more long drawn out, effects. Actually one of the opening strikes in this war uses a high altitude nuke for an EMP. Just watched it, short of first aid for the immediate victims, as per priorities, what has been said, water, food, shelter, security, and in that order. Nukes with fallout though, air..filters, deep shelter, that's about it that might work.
https://www.youtube.com/watch?v=_MCbTvoNrAg