mystery bag

Etymology 1
From +.

Noun

 * 1) A bag whose contents are unknown.
 * 2) * 2010, Barbara Isaacs, Sandy Green (series editor), Bringing the Montessori Approach to Your Early Years Practice, Second edition, |%22mystery+bags%22+-intitle:%22%22+-inauthor:%22%22&hl=en&sa=X&ei=eby5T8XxNKTFmQWz_92vCQ&redir_esc=y#v=onepage&q=%22mystery%20bag%22|%22mystery%20bags%22%20-intitle%3A%22%22%20-inauthor%3A%22%22&f=false page 43,
 * An activity in this area, which focuses on the tactile aspects, without using visual discrimination, is the mystery bag. This bag contains sets of matching objects; the child is expected to pair them by feel.
 * 1) A surprise package randomly picked, a lucky dip.
 * 2) A non-specific mixed lot of a product at the supplier's choice.
 * 1) A surprise package randomly picked, a lucky dip.
 * 2) A non-specific mixed lot of a product at the supplier's choice.

Etymology 2
From c. 19 British rhyming slang for, influenced by sense “bag whose contents are unknown”.

Noun

 * 1)  A sausage.
 * 2)  A pie.
 * 1)  A pie.