Keychains and Boat Documents can refer to several things, but generally it concerns:

Nautical keychains : practical and decorative items designed for boat keys. They're often buoyant (so they won't get lost in the water) and saltwater resistant.

Boat documents : the set of mandatory documents to be kept on board, such as:

• Navigation license (or registration certificate)
• Insurance (mandatory third party liability insurance for some categories)
• Boating license (if required for the type of vessel and distance from the coast)
• Safety certificate (for vessels above certain dimensions)
• RINA (Italian Naval Register) or other certificates of suitability, if necessary
• Safety equipment (updated register)
• CE Conformity Document (for newer boats)

Waterproof cases or pouches are often used to store these documents safely on the boat.