First DWI and First Possesion. Help.

The last I remember, I was at a bar. Then, I was woke up by an ambulance driver. I was asleep behind the wheel of my truck at an intersection, and didn't know where I was. I took my key out of the ignition and gave it to the ambulance driver. When the cops pulled up, I was sitting in my truck. It wasn't running and I didn't have the keys. He found a small bag of drugs in my pocket that I don't remember how it got there. I can't recall doing any drugs that night, or for at least a year for that matter. It was less than a gram. What is my best and worst case scenario?