I don't know if anyone is interested in this, but I just discovered it this morning.  If you need someplace to squirrel away some cash, you can utilize your luggage tags.   When you fold them, you end up with a pocket ( see photo ).   Laminate the tag with clear tape, leaving that one edge open.   Hide some cash in the tag, and seal it up. Staple it to your carry on only.   Though I doubt the tag will come off, why chance it.    You can even make an extra one and leave it attached to your luggage.   Who would know ?     I've read too many complaints about thefts on ships lately, so I guess I am getting a little paranoid.  Sorry.

Having trouble with image ( thanks IOS 8 ),    but you get the idea