The ol' "Ship in a Bottle" trick...

Peel the label off the bottle. There is usually a little stickiness left on so that is where I cut the bottle to make a 'door'. Make your label & apply to the bottle. I usually use clear contact paper to apply the label. Just make sure it is stuck on well enough to go through the mail. I've had fun comments hearing how friends & college students have tried to get the contents out! Make sure if you plan to mail the bottle, you go by all the rules...such as nothing inflamable or it will have to go by land and take longer to get where you want it. Bummer....fingernail polish cannot by mailed as it is flammable. There's no end to the possibilites of what to put in, though.