How can two people be found in a vehicle that crashed a third in the alley drugs found nobody knows who was driving and only one person charged?

OK, the most important response to this question is that charged is very different than convicted.  Which is a short way of answering your entire question.  To charge someone with a crime the police need probable cause.  That means they have specific and articulable facts that led them to believe you committed a crime.  To convict someone you need proof beyond a reasonable doubt.  That is the highest burden of proof in the court system.  You have been charged, that does not mean you will be convicted.   Now let's unpack your case.  They can establish you were driving through circumstantial evidence, for instance, was it your car?  Don't answer that unless you are speaking confidentially with an attorney.  Secondly, have the police seen you operating that car in the past.  The same with the possession.  If they had information that you were dealing the specific drugs found that would be circumstantial evidence that the drugs were yours.  They can also prove it by looking through the bag and finding your belongings or identification.  A common method of proof is when the ID/Wallet of the accused is found in the backpack.   Importantly, circumstantial evidence is sufficient for a conviction but that does not make it easy.  As you point out in your summation of the facts there are some discrepancies that would argue against your having committed the crime.  Importantly, there are some assertions that may flat out be incorrect.  That would call the officer's credibility into question.   All of that being said, if you are charged in this matter you need experienced representation.  Trial on these issues is not something to be attempted by people without experience.  TV is not a fair representation of trial and a trial can be one on small issues an untrained eye may miss.  Talk to a local experienced defense attorney and let them walk you through the various outcomes and expectations.