I think the urine reference is that there is always traces of urine (improper/thorough wiping) if clothes have been worn. I think they were trying to confirm whether they were clothes that had been worn at all or packed clean clothing BUT...the detective did say that they seemed to have been freshly laundered (to the best of my recollection).
Makes me wonder if perhaps, Sierra was leaving a "trail" of some sort?
The cell phone being found on the opposite side of the road, sounds like it was tossed out a window of a faster moving vehicle.
The bag, being found on the side of the road but, unable to confirm if it was the opposite side of the road, leaves wondering if it was done by Sierra or the driver?