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:
CJ-Curry: "I'll have a A please Natalie247."
Natalie247: "Which A is popular container for regular or large geocaches?"
CJ-Curry: "It's A...."
Natalie247: "Correct - you might want to store that away for later to see where i go with it."