Sure, GPS is available and very useful, but what happens if suddenly they no longer work? Obviously, you will have to turn to using physical maps to help guide you to the Stasi to denounce your "friends". 
These East German vinyl map cases are perfect for just that! 

These map cases have two separate compartments to hold plenty of maps and documents, as well as a fold-out map window to keep your maps dry while in use. 
 
There are also slots to hold your pens and pencils, as well as various other straps that I am unsure to what they can be used for.
 
Simply sling this over your shoulder with the detachable strap and you'll be ready to go!
As seen in the photos, these can hold quite a lot of items. I was able to fit four 200-300 page books in one. 
 
These are used surplus, so please expect some fraying, stains, markings, and/or surface rust. Otherwise, these are ready to be used out of the box.