I am not an artist or musician, and I have not engaged in any original research. Am I at a disadvantage for not submitting supplementary material? Should I submit something else?

There is no need to submit supplementary material. The vast majority of our students are admitted on the basis of required documents alone. For a very small number of exceptionally talented artists, musicians, and researchers, supplementary material may be useful to communicate information that cannot be conveyed adequately in the rest of the application. See the guidelines about Supplementary Materials for more information.