Holdger explains well how to add AI ships. perhaps the largest single add on is the FreeFlow series ...both Florida and Bermuda add tons of AI ships of all kinds, also you can get sailboats added to the coast of Italy, ferries for Cyprus, and Seattle, a few ferries for east Coast uSA, the circle line boats for New York Harbour, boats of all kinds for the sound off New Zealand, more boats from the Bora Bora add ons and some of the other pacific islands add ons, ships for the Great Lakes, and you will see there is a huge variety of ships to pick from now in the shipyard.....plus many you can pilot and operate yourself. If you have the Lago Venice, it has many ships including the vaporettas that run on schedule up and down the Grand Canal....for cars, well there are quite a few that add the, one of the very best for FS9 is the Payware Portland Airport add on it has busy AI plane and truck and car traffic to the degree that if you park yourself anywhere along the public approach roads, you will literally feel you are in the real portland itself.
the Visual Flight France series all have add on ships and boats...the ones that are on coasts...
Also Holger's payware Misty Fjords and freeware Glacier Bay add ons have great AI or there are ones you can add..ditto his Victoria and Vancouver add ons.
enjoy and see the world come alive.