Not much you can do except contact the police nearest where it was left. The police will also want its serial number. If you registered it with Apple, you can look up your https://supportprofile.apple.com/ If you have your serial number, you can report it to AppleCare as lost. Then hopefully they can at least try to track it down if someone tries to bring it in for service. But that's a long shot. In the future, if you don't want to enable iCloud for Find My Mac, there is always Lapcop and Lojack. Lastly, always backup your data:
https://discussions.apple.com/docs/DOC-1992