Going through the last of my father's effects has made me realise something important - although I was never a great student of Chemistry, my father's insistence that I study it, along with various aspects of Engineering (at which I was much better) now makes a lot more sense.
The problem is - how do you prepare? How do you rebuild? How do you know what materials to use? How do you get what you need once all that you can scavenge has been taken? How do you avoid the mistakes of the past, and get to what you need without several centuries of rediscovery of technologies?
As a scenario: A star close enough becomes a supernova. It is far enough away that we avoid the more serious types of damage, yet we suffer an extended or frequent electromagnetic pulse. 99.99999% of electronics are destroyed very quickly. Infrastructure breaks down, computers are useless, the world stops - or at least the parts of the world dependent on electricity, computers, and all mod-cons. Third world countries are alright - people don't have what they would classify as luxuries, and what we would as essentials. Valves, now nearly obselete, become needed again. Could you make a valve based radio? Could you make a valve?
Would you, in short, know where to start? Do you actually have paper copies of such things? Having them saved on your computer is no good - your computer is little more than a large brick.
Could you make aluminium from clay? It's relatively easy if you know how and have some knowledge of chemistry, but an impossible task if you regard ignorance as better than learning.
Could you even make iron tools? Could you, given the need, find a patch of iron ore, smelt it, build a forge, make the simple tools needed to make the more complex tools?
The vikings were able to get iron from 1% ore - incredibly low yields, but it is there for the taking.
Not necessary, you might scoff... But once you've run out of things to scavenge, once no more spare parts can be found, once you've used something like petrol up, what then?
Stills are easy enough to make, but do you know how to modify an engine properly? What about gaskets and pistons that will corrode because they were designed for hydrocarbons rather than ethanol?
Do you have anything to trade for the bits that you need?
My library acquistion continues, as does my gardening, my acquisition of skills.