1. A belly button.
  2. A wine stain on your shirt. 
  3. Closed containers.
  4. A 21–year–old person's mouth. 
  5. An old hat.
  6. Hospital Dixie cups.
  7. An expensive beer—people will assume you aren't a Penn student.
  8. A bucket.
  9. Cups, Mr. Balloon Hands.
  10. Water bottle—it's actually water, hydration is important when you're on ecstasy.

Photo credit: Flickr