You can go to the Bacardi factory almost free if you don't book through the ship. Just get into Old San Juan and get to the water taxi, take it across and catch a cab to the factory. Cost about $5 round trip last time I was there. Factory tour is free, with free samples.
There is another rum factory called Don Q's right beside the water taxi terminal. It's also free with free drinks.
Serenade OTS 10/2005
Freedom OTS 9/2007 and 4/2008
Majesty OTS 2/2009
Monarch OTS over and over and over again
Carnival Imagination 5/2009
Oasis OTS 2/2010
Grandeur OTS 3/2010