The question that is the most prevalent for me in this case is, that there is a big "why" about it.
Lets just assume for a sec global conflict does indeed occur, the scenario presented will most likely wipe you out anyway in some form or another.
Therefore I life my live as good as I can, idenpendently of immenent doom.
Furthermore, if there is one thing Corona has taught us, its how to life comfortably at home and improved efficiency to think of food as "food for a week" or even "food for a month", so yeah, if anything at all I stopped doing smaller trips to the supermarket and now go for bigger hauls.
Finally, I still do believe in the good of community and thus am sure, that within a short period of time, local communities will form. Sure Mad Max et al is a possible scenario, but I rather believe that humanity as whole will muster through.
This entire world we live in is based on mutual trust in people and therefore I am sure we can rebuild in any case. If we cant, no preparation in the world will suffice.