Lots of military and espionage organizations have escape and evade kits that they give to their operatives who are in hostile territory. Information on local plants that can be eaten, maps, places or roads to avoid. Today they are usually printed on tyvek.
In World War II, they frequently printed maps and information on silk, because it wouldn't ruin if it got wet and unlike paper it wouldn't make much noise while viewed. The maps were sewn into linings of suits, printed on the inside of ties, and various other places. Very clever.
Last week, I ran across an article about taking that idea to the next level. Apparently during World War II, the Germans allowed certain items to be given to POW's through charity groups. One item deemed acceptable was board games. So Waddington's, a company in the UK, made 'special' Monopoly games to be distributed to POW's.
ps. If you want to read the entire article, here's the link:http://abcnews.go.com/Technology/monopolys-hidden-escape-maps-free-pows/Story?id=8605905&page=1