Imagine this

Imagine walking into your local supermarket to buy a pint of milk and being faced with a label on the shelf reading something like, “This product may contain nuts and will cost between 43p and 62p depending on consumer demand, best of luck and we hope you reach the checkout safely and in one piece. Signed, your pal Vince”.
Never happen I suppose. But imagine buying a usb charger for your Kindle and getting a free gift with it which you don't understand how to use.
At first I wondered about a terrorist plot (oh bugger, said it now, police at the door), then I thought about jewellery or even a thing to store forgotten passwords in.
What is this thing?