Depends on where I lived.
Born outside a city in Sweden so "child war-time preparation" would had been to hide in the forest (or in my own little "dirt vault" under some grass) I guess.
I have no idea about the radiation so let's just assume it's no issue where I am and that ~everyone else is dead. Or maybe not. I haven't really played Fallout damnit! I've bought 3 and New Vegas and I've got the others for free on GOG but I've just dipped my toe into Fallout 3.
Step 1: Get radiation suit.
Step 2: Find a cat. Life is meaningless without a cat. (Yeah, 36 year old and forever single, still virgin, don't judge me - cat's rule!)
And then I was thinking farming, I'm vegan and all. But it's a game with guns ..
Step 3: Find a Stridsbåt 90 somewhere, they are bound to be one somewhere, at this time and age it should be nuclear powered and let's just assume Sweden wasn't ruled by environmentalists socialist feminazis, ok?! (Stridsbåt 90:
https://youtu.be/6sH-M_awQ7g?t=31s https://www.youtube.com/watch?v=rfpXFKKKl4Q
https://www.youtube.com/watch?v=9I42PVJtOlc - It's my zombie fighting platform of choice.)
(???!)
Step 4: Pick up some board-games and some nice people with the boat, then find an abandoned container ship a la water-world (love that film!) instead.
Step 5: Enter container ship with newly found friends, board-games, some cats, maybe put some dirt and plants and grow things on it, some farming equipment such as a tractor or two.
Step 6: Set sail on some island out in the Pacific, stay there, hang around and appreciate a free life. (This is to feel quite safe from any nukes.)
But I guess more likely I'd die early due to my low experience with the game and hence no awareness or experiences whatsoever about what I've gotten myself into.
Turns out I need to play a lot more Fallout or I'm dead!