I think about this all the time. Usually when I'm sitting on the toilet. I'd grab my external (it's my life's work), my cats (I love them), and all the video games my arms can carry (because if I sold them, I'd be fucking rich). If I had time to make a few trips to and from the car, I'd make sure every video game and system I currently have is in there, including the box of atari in the basement. You never know when you need a Breakout jam. I'd also try to save some of my posters. Especially that epic treasure that lurks behind my bedroom door. I'd want to save some of those just because of the time, effort and money that went into collecting them all. And I'd grab my rats. And the two books of movies we have. Again, that one is because we could sell that shit for big money. Plus, it would take a few good, solid months to watch all of that and I might need something to do while I wait for the impending apocalypse.
Completely unrelated but: I have a physical this morning. Not awesome.