Books are good... Well, many books are... I've been slack recently with increasing my library. It still happens, but if you get a book that covers a lot in a particular field, unless you need more detail, you don't need lots... Plus... If you get to the stage where your personal library is needed to help rebuild civilisation, you don't need a lot of depth and a single subject... Better to get depth on a couple, and breadth on many - Jack of all trades, master of a couple.
I've found that my collection is too small when it comes to veterinary medicine - and a little short for human medicine - so they're both on the list... I could do with a few more books directly aimed at recreating... but...
The problem is - Human History is, has been, and probably will always be about Trade.
If we were hit with a cataclysm that took us backward a couple of centuries - we'd have the knowledge on how to rebuild, but would we have the raw materials? How much processing is involved in all the "raw" materials that come to hand... if you build electronic equipment, the individual parts come from elsewhere. If you build the parts - the material for the parts has to be found... Exotic techniques might be able to be cobbled together, but do you know a local source of Indium that you could mine? Or, let's face it, Gold? Copper isn't easy to come by, but at least you'd be able to pull it out of destroyed houses, wires and cabling, but then what?
Tin is a very important metal historically in various alloys - but do you know where to get it from? At least Middle Eastern traders two thousand (and more) years ago could get it from England... Two thousand years ago, trade routes did span from Asia through to Europe, and at least part way into Africa...
Sulfur is a very useful element for making other things, but you tend to find it more in volcanic areas. Which reminds me - I have to find alternatives for catalysing ethanol into diethyl ether - from alcohol to anaesthetic.
Logistically speaking, TEOTWAWKI is going to be a bitch...