Update: February 24, 2018
The 'Disco Ball': Created by Rocket Lab founder and CEO Peter Beck, the Humanity Star is a geodesic sphere made from carbon fibre with 76 highly reflective panels. It spins rapidly, reflecting the sun’s rays back to Earth, creating a flashing light that can be seen against a backdrop of stars. Visible for a few seconds, every 90 minutes, each night, for the next several months.
Criticisms: Wikipedia, Caleb Scharf in Scientific America.
Update: February 21, 2018
Throughout history a number of odd or useless things have been sent into space. Commercial ventures seem to top the list for 'bad ideas' placing profit and sanity over professionalism and safety.
In 2005 a gold-plated scandium six-iron golf club from Element 21, several golf balls, an equipment bag, tee and specially-built platform were hauled to the station last September on a Russian space freighter.
See anything wrong with this picture?
Indeed there were delays approving the stunt and it was cancelled eventually due to safety concerns. The idea was that the balls were equipped with transmitters that would enable golfers to follow its flight around the world at the company's Web site, because that's something golfers would like to do.
Suggested by user "Organic Marble" are the Coke dispensing machines and the Pepsi can shaped inflatable.
The yellow tinted Coke machine, an unfortunate color choice considering where the water comes from.
Later flights included a more traditional color scheme with a new set of problems.
The machine also included a number of complicated accessories necessary for its operation. Personally autographed photo of Vladimir G. Titov examining the refills for the pop machine.
Rare (and low resolution) footage from YouTube showing BTS of the inflatable Pepsi can commercial, with interviews and extra info (15 mins.). Video footage of the can and banner was shot both inside and outside Mir space station but the commercial never aired because Pepsi later changed the design of the can.
You would really have to be noodles to think Nissin Noodles would be a good idea for space consumption, boiling water, chop sticks, or just mash them and eat it like toothpaste.
Earlier space flights were kinder to their human occupants, it was non-human lifeforms that suffered indignities.
The Russian Tortoise is an endangered species so it seems as though a better choice could have been made. The launch of Fruit Flies didn't seem particularly adventurous.
Here is a photo of Miss Baker, she was accompanied by Neurospora, samples of human blood; E. coli; onions; mustard and corn seeds; Drosophila pupae; yeast, and sea urchin eggs and sperm.
Which is sillier, traveling with E. Coli or urchin sperm?
The reason cheese was sent into orbit is because it was a maiden flight with many untested calculations, so they didn't want to risk anything too valuable.
Other silly things included:
The Astronaut's Checklist (Link to a .PDF of one of the EVA Checklists) for Apollo 12 had centerfolds of Playboy Playmates added to it. The photos and captions are:
Angela Dorian (Miss September 1967) with the line "Seen any interesting hills & valleys?"
Reagan Wilson (Miss October 1967) was displayed as a "Preferred tether partner."
Cynthia Myers (Miss December 1968) and "Don't forget—describe the protuberances."
Leslie Bianchini (Miss January 1969) and "Survey her activity."
DeDe Lind (Miss August 1967) titled "Map of a Heavenly Body".
Coca Cola spent \$250K followed by Pepsi who spent $14M to develop cans for dispensing their beverages in space. The Challenger shuttle was sent into orbit in 1985 with four cans of each cola. The five-person crew tested the drinks out and hated both brands.
I'm not so sure it was silly to take Luke Skywalker's Light Saber into space and the Russians carry TP-28 triple barreled guns in case they run into bears and wolves upon landing.
The most useless thing was a shellaced hamburger.
Buzz Lightyear joined the crew of the STS-124 space shuttle mission, launched May 31, 2008.
Also silly was a Obama Bobblehead but it didn't pass the stratosphere and it's reason was to raise funds for reelection.
Update: February 21, 2018 - Starman Payload. New upload to Musk's Instagram account.
Update: February 6, 2018: Here's the video, car closeup at the end.