Noted numismatic author and specialist Mr. Fred Schwan has frequently listed his favorite Second World War collectible as the common Allied Military Currency (AMC) 2 Franc note.  To him, this note represents "history in your hands", as so many of these went with Allied troops on D-Day, to allow a medium of exchange for commerce.  These notes are fairly common and can be obtained in excellent condition for very reasonable prices, so it is not their rarity that makes them valuable; it is their connection to a tremendous event in history.