A small 50ml pill container.
This cache is part of the Blockbuster A to Z series.
An old 80's gameshow in which contestants had to pick letters and answer questions relating to that letter to get across the board and win.
If we were doing a modern day geocache version of this I would imagine it would go:
Kev the Orienteer: "I'll have a B please Natalie247."
Natalie247: "Which B is An acronym often used by geocache owners to communicate to other geocachers that you will need to bring your writing utensil in order to sign the cache logbook ?"
Kev the Orienteer: "It's B....."
Natalie247: "Correct - you might want to store that away for later to see where i go with it."