Is your appendix a functionless evolutionary vestige?

Essentially yes: In people, the appendix seems to serve no good purpose. In animals that eat a lot of high Cellulose foods (e.g., grass), the appendix is larger and seems to serve as a storage area in the gut for difficult-to-digest foods. The appendix only seems to cause problems (i.e., appendicitis) in humans. That said, it can be used by surgeons to create a specialized vascularized conduit (e.g., for urine).