A hidden stash whose location is found only by following clues. A traditional letterbox contains, at minimum, a rubber stamp and log. Other items that may be included are a page describing letterboxing for anyone who accidentally finds the box, stamped, pre-addressed postcards to be mailed to the box owner to let them know the box has been found or needs maintenance, a First Finder's certificate, an ink pad and a a pencil or pen. A letterbox's contents are usually packed in two sturdy zip lock plastic bags, and then placed in a waterproof container to protect from the elements. See drive-by letterbox , hitchhiker, letterbook, mystery letterbox, personal letterbox, traveller, urban letterbox , virtual letterbox, letterbox series.