Lore is that it was Elon's personal Roadster. It was used on the launch to provide weight necessary to compensate for future launches with a payload. Batteries may have been included if necessary to make the wieght.
Starman was added as an afterthought. He is a dummy with sensors and a representation of the space suit that future Space X Astronauts will wear.
It was perhaps one of the most inventive and effective marketing stunts ever pulled off. Symbolizes the plans of Space X to go to Mars...and beyond. Also tied together the close relationship between Space X and Tesla. Brilliant!
Not sure if Starman wore a watch or not