Say you want to add a comment that will print on the receipt on the sale of specific stock items, you can do it.
In stock maintenance, pressing the Notes button (near bottom right), for a stock item. This will bring up the stock notes box. Put a note in here starting with "^" and it will appear on the receipt.
For example, say you put in ^Next week, this item will not be available. This message will appear at the bottom of the receipt.