Log book
From GeoWiki
A physical means to record a visit to a geocache. Stored in the geocache.
May take several different forms. They can be a small spiral log book, an exercise book, a long strip of paper, or any other clever means of recording a visit.
Donkey uses a pack of cards!
The log book is not always accompanied by a writing implement, so best to always have your own. Or better yet, have a signature item to put in each logbook. Some use a custom or novelty stamp, others use stickers they have printed at home.