If it was passcoded, then the information on the iPod should be safe and encrypted. If you had Find My iPod turned on in the iCloud settings, I'd keep checking iCloud.com to see if the iPod connects to a wi-fi network. If so, you can choose to erase it remotely, or contact local law enforcement and try to recover it based on its location.
Otherwise, if all else fails, it'll likely just get erased by the thief and resold to a pawn shop iPod something. If you have the serial number of the iPod somewhere, you may be able to report it and see if it turns up at t local pawn stores.
Otherwise, your information should be encrypted, so hopefully it won't be able to be easily accessed. Good luck.