I found this sitting half filled out while tidying up before my trip. I thought it'd be entertaining to post with a few answers from Vogon, although which ones he provided will be left as an exercise for the reader.

If I were a month, I would be: August.
If I were a day of the week, I would be: Tuesday.
If I were a time of day, I would be: afternoon.
If I were a planet, I would be: S Ori 70.
If I were a sea animal, I would be: Stenorhynchus seticornis, arrow crab.
If I were a direction, I would be: northwest.
If I were a piece of furniture, I would be: an Eames wire chair.
If I were a historical figure, I would be: Lysistrata.
If I were a liquid, I would be: mercury.
If I were a stone, I would be: opal.
If I were a tree, I would be: Cercis canadensis, Eastern Redbud, cultivar 'Forest Pansy'.
If I were a bird, I would be: Psitticus erithacus erithacus, African Grey Parrot.
If I were a tool, I would be: a seam ripper.
If I were a flower/plant, I would be: Vanilla planifolia, Vanilla orchid.
If I were a kind of weather, I would be: virga.
If I were a mythical creature, I would be: a Faun.
If I were a musical instrument, I would be: a violin.
If I were an animal, I would be: a monkey.
If I were a color, I would be: grey.
If I were an emotion, I would be: delight. [insert Sandman joke here]
If I were a vegetable, I would be: asparagus.
If I were a sound, I would be: a waveform with mirror symmetry.
If I were an element, I would be: fire.
If I were a car, I would be: parked.
If I were a song, I would be: "Doun" by Vanessa-Mae (iTunes Music Store)
If I were a movie, I would be directed by: Jean-Pierre Jeunet.
If I were a book, I would be written by: Ursula K. LeGuin.
If I were a food, I would be: mousse.
If I were a place, I would be: home.
If I were a material, I would be: moleskin.
If I were a taste, I would be: orange honey.
If I were a scent, I would be: Mexican vanilla.
If I were a word, I would be: callipygian.
If I were a body part, I would be: a clitoris.
If I were a facial expression, I would be: a smirk.
If I were a subject in school, I would be: Latin.
If I were a shape, I would be: a heptagon.


edited to add: Ah, I'll avoid the suspense and tell you which ones were his answers. He said I'd be a Vanilla orchid, a violin, mousse, and a heptagon. He agreed I'd be the color grey and thought I'd be a frown, not a smirk.