FLOTSAM refers to wreckage or cargo from ships that is found afloat or washed up by the ocean. It is also used for people and things considered worthless: “Before putting their house on the market, the owners cleared it of all magazines, newspapers and other flotsam. The root is in the Anglo-Norman French from the verb “to float.”
JETSAM isn’t normally used for people but rather for unwanted cargo that has been thrown overboard and then has washed ashore. It derives from the 16th century English word “jettison.”
Interestingly, when Googling for an image, I discovered a rock band exists called Flotsam and Jetsam. I wonder if they were tossed off a ship.