Would I be committing a crime in this situation?

December 6, 2013
More details to this question:
I go to a fast food restaurant and go through the drive-thru, and when I’m handed my bag of food I set it in the passenger seat and go home. Once I get home I look in the bag and instead of food there’s a couple thousand dollars. The employee accidentally handed me the bag that was supposed to go to the bank. The manger quickly figures out that it was me who got the bag because I paid with a debit card and my food was still there. They call my house and I refuse to give it back, because I figure that I was given it so I can keep it if I want. Am I committing a crime?