I would have made a cursory effort to get some contact info from it, but if it were locked or there was no information, I would would have turned it into the McDonalds management. If I did get in contact with the owner, I would see whether they would want to pick it up at McDs or from my possession.
In April 2009 I lost my iphone at 3am. In a Taxi cab. In NYC. While I was drunk. The next fare not only found my phone, but called multiple people in my contact list until it was relayed to me that my phone was found the next morning. The next evening I traveled into the city and picked up my phone, fully charged at a residence on the lower west side. Yes, I know I was lucky but I would certainly try to pay it forward.