Possible Clues:

• Checkout printout
• Stub, at times
• Ticket stub, e.g.
• Confirmation of purchase of extremely rare chair, say
• A slip you had to pay for?
• Expense report need
• Acknowledgement about country residence, we hear
• Written acknowledgement of old cook's directions
• The price not hard to work out - from this bit of paper?
• Acknowledgment given when time-piece runs backwards