I'm in the Seattle area and we are always told to be prepared for a major earthquake by having food medicine water etc stored in our homes and in our cars in case we're on the road when the big one hits. It could be that the JW's are getting prepared for that especially since they think Armegeddon will follow on the heals of a major disaster anyway so they are doubly motivated about being prepared. The thing is, how long can you put off the inevitable. That is, you can't store that much food or water, you'd eventually run out of it in a long term situation like the "tribulation". Anyone who appeared to be surviving would be targeted by those who were without.
Back in the Pre 1975 days. There were people in our hall that had literature buried in plastic soap bottles in their back yards so that when there was a "Ban" on the preaching work or whatever, they'd have a stash of literature to keep them going. I often wondered if some of that stuff is still out there today or if anyone ever found it and wondered what was going on. That would be a great assembly experience or urban legend....someone became a Witness after finding the truth buried in a soap bottle in their back yard.