One good example of symbolism is Arthur Dent, one of the last remaining Humans from Earth. He represents all of humanity, and his life in the beginning of the book echoes the eventual fate of the planet itself: his house is scheduled for demolition, and he was not informed, just like the Earth is scheduled to be destroyed. The senseless bureaucracy of Earth compares to the Vogons, while Arthur, being an untraveled, meek human, compares to Earth; the planet is not aware of other life in the galaxy and is extremely self-absorbed, incapable of having any substantial effect on a larger scale.
Arthur blinked at the screens and felt he was missing something important. Suddenly he realized what it was.
"Is there any tea on this spaceship?" he asked.
More of the planet was unfolding beneath them as the Heart of Gold streaked along its orbital path.
(Adams, The Hitchhiker's Guide to the Galaxy, Google Books)
Here, Arthur ignored the more impressive facts of being in a spaceship in another Solar System, with alien beings, and focuses on tea; this symbolizes the Earth and its refusal to accept or understand the larger scope of the galaxy and its inhabitants. Arthur represents the whole of humanity, not in a negative way, but as a simpler, more naive race compared.