If you sail the world, do you accually need any passports, visas and so on? Please educate me.
You may need more than this.
As others said, countries and ports vary in how diligent they are actually checking, but here are some common extras:
1. In some Med countries, you are not allowed to enter w/o a VHF certificate. Don't ask me why - though you can see the safety aspect.
2. You are supposed to carry a Crew List, matched against passports.
3. Theoretically - though this is probably the least commonly checked - a port may require current insurance papers.
4. The boat papers must be complete if entering e.g. EU, with specification of country of origin. If US-registered, duty and VAT is payable if kept in EU waters beyond 6 mnths, to the papers are stamped on date of first entry.
5. Worth looking out for: implementation is only tentative so far, but e.g. EU countries are increasingly steering towards a "skipper certificate", i.e. you need papers to show that you are entitled to skipper a boat the size of yours. Normally, this means that if you are allowed in your home country, they must accept you.
As you may have guessed, there are parts of the world - too many to list - where the request for "papers" is a great pretext for extracting bribes, so it really pays to have as much as possible to beat them over the head with.