This is the list of documents that we brought with us on our trip, the list will most likely grow in the future but till now it works as a pretty good skeleton for us.

Personal

Passport
Driver license
Certificates related to yachting
European health insurance card (Europeiska sjukförsäkringskortet)
Vaccination documents
Extended travel insurance documents

Boat

Purchasing contract (with VAT included)
International certificate (the yellow book from SXK)
Insurance documents
Crew list
Manuals for more or less everything on the boat.