When preparing for any large-scale emergency or disaster scenario our initial tendency is to seek out the most basic necessities for survival: food, water, shelter. Those serious about survival expand these necessities to include protection, first-aid, mobility, etc. I believe one of the most important tools to include in any survival plan is a smart phone capable of offline card storage.
In my profession, I am attached to my smart phone. I depend upon it to work as much as my Leatherman while backpacking. I also know that during a large-scale emergency or a TEOTWAWKI scenario, a cell phone for the purpose of calling might be completely ineffective. Cell towers, satellites, and the Internet require huge amounts of manpower and infrastructure to maintain. However, if these go down your phone can still be used as a wealth of knowledge that can literally save your life.