If civilization collapses and you live on your own, you will not have much data to store, organize, etc. Therefore a computer won't be that useful to you. What will be a priority to you will be to survive, which essentially means how to get drinking water and nutrition, as well as territorial control and self defense. A computer will be useful to you if you become a ruler that is responsible for the census, taxation,…
Having a large collection of offline reference books, maps, and music/movies for entertainment would still be desirable for those who can find a way to power/charge a device. Rather than building a 'collapse OS', maybe just hoard some reference material, and have a plan (and multiple backup plans) for powering/charging devices in the absense of a power grid or fuel for generators/vehicles. I don't think anyone's goin…
Paper maps will be far more practical.
First targets going down in a global war will be GPS, Galileo, Glonass, etc. so all those systems will go offline right away.
All power will go to water pumps, heating, air conditioning, mining, etc.