2001: A Space Odyssey References
This easter egg is found in Season 1, Episode 8a titled, "Sandy's Rocket".
When SpongeBob and Patrick are messing around in Sandy’s space ship and accidentally launch the rocket, they begin falling through the ship and almost hit the ground before gravity gives way and they begin to float.
During the scene when we see them both floating and looking out the window some of the items on the ship floating around them are referencing the 1968 sci-fi movie, 2001: A Space Odyssey.
The items we see are a pencil, in reference to the pen scene from 2001 during the docking scene and a book that is actually titled, “2001”. Unlike all other items in this scene which include a toolbox, spindle and wrench, the pencil and book are quickly taken out of the scene giving viewers only a couple of seconds to catch the reference.