Christmas Seals have been called a "back of the book" collectable, as they are listed in the back of stamp catalogs. If that is so, then the following material related to Christmas Seal collecting might be called "back of the back of the book"

Milk Bottle Collars

1940 with green inscription on right 3.50

1941 3.50

1945 3.50

1946 grey blue 3.50

 

Christmas Seal Transit Passes - wanted