What is the prop that has been in every science fiction film and show?

According to production designer John Iacovelli on the commentary of the Babylon 5 pilot, a pervasive group of prop makers nicknamed "The Woodland Creatures" has been sure to include a certain prop in pretty much every sci-fi series and film, which is smaller than a bread box and larger than a soda can. Is this true? What is the prop?|||THE BEST PROP IS "THE UNKNOWN".|||not sure......