If there has been an accident, usually police will take a peak inside the car to see if theres is evidence of drugs or alchohol in the car it's standard.
I was side swiped by a semis yesterday & as I was giving 1 of the responding officers my info a female cop started going through my car & even popped the trunk & started pulling out my belongings. Was she aloud to do that? And why?
They can make a visual inspection of items "in plain sight".
She is not "allowed" to open your trunk or go through your belongings without a warrant or "probable cause".
Even if you appeared "under the influence", it would not usually be "probable cause" to open your trunk.