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:
SpyDude13: "I'll have a P please Natalie247."
Natalie247: "Which P is given to members who have paid to have more features available to them than Basic members?"
SpyDude13: "It's P....."
Natalie247: "Correct - you might want to store that away for later to see where i go with it."