I see what you are thinking, also riding the trend for ridiculously expensive things, like £100 bagels or whatever. I think you'll have trouble with security if you put any serious money in there. How are you going to stop someone from opening it and copying the keys and then wrapping it up again? Granted, you can buy tamper evident tape off the Internet but I'm not sure that fixes it?
You could embed the paper wallet in the chocolate somehow, so that it would have to be eaten to get to it.