Like everyone else, I've got important documents that I want to be preserved across a disaster. I've taken a different approach, though. I've noticed that there really doesn't seem to be much in the way of 'unreplaceable originals' any more. Deeds, birth, and death certificates are recorded, with certified copies available for a fee. Duplicate documents of various sorts can be reproduced with official seals or stamps. The key is to know what these documents are, and where to go to get the duplicates.
I've gone to electronic storage. I've scanned in the deed and mortgage paperwork, the birth and death certificates, and the supporting tax documents. For the past dozen years, when I prepared a tax return I used software, and 'printed' the return to a PDF file, which I then printed and submitted (until we moved to electronic submissions). I've even scanned the contents of wallets and purses, capturing all those cards, front & back (the phone number to report stolen cards is on the back of many cards).
All this data, along with electronic copies of financial records, statements, and whatnot goes into files that are on an encrypted disk image on the computer. The encrypted image is backed up automatically, to external storage, and to flash drives. One of the flash drives is on the little keyring I always have with me.
This way, I can always make copies of important documents immediately. If I need to get a certified copy, I know which bank, county recorder, or other agency to contact, as that's on the image of the documents.