From left to right: Galileo, Juno (Roman goddess) and Jupiter (Roman god) are embodied in Lego on the Juno spacecraft
My favourite is probably the brainwaves of Ann Druyan. This was a recording made on an EEG machine and was included on the golden records that were sent to space aboard Voyager 1 and 2 in 1977. Ann Druyan is a science writer and TV producer who was part of the team responsible for choosing the sounds and music that went on the record.
During the recording, Druyan had a list of topics to think about, including the history of Earth, the difficulties affecting human civilisation and what it is like to fall in love. The Voyager program cost £600m but the brainwave recording was effectively free. My second favourite is the Lego minifigure of the astronomer Galileo, which arrived at Jupiter aboard the Juno spacecraft.