I forgot this is right up your alley. I was under the impression that drugs were one thing that it didn't matter who has it. If you are in the area, you can be arrested and charged, no?
Depends on state law, but a person has to possess the drugs to be charged. That definition varies by state, but it usually requires: 1. They know the drugs are there and know of their nature (is that they are illegal), and 2. They had the ability to access them quickly. The knowing is the hard part.
I have a lot of cases that get declined because the drugs are in a pill bottle or non-clear baggie and we cannot show who they belonged to or that either party knew about them. And really, you want to be able to say who they belong to. If you don't, it is almost impossible to prove.