In my experience Ryanair only accept Euro and Sterling cash on board.
If it wasn't coz I like your handle, I'd call you something......
If you have flown outside UK/Ireland you'd know they accept local currencies. What they put it the red bags... I don't know. They say money. I am with Aluminum Shuffler, never seen any accompanying paper work. While aviation is a lot about trust in others, I think it's within every captain's right to refuse those bags. The red bag system is probably the cheapest solution to ship the money, hence its use.