Cosmo Canyon song
You can play the Cosmo Canyon song on your own by going to Tifa's house in Nibelheim. Then, press , , , , , , , + , , + , + , + , + , , + , + , + , , + , + , , , , , , , and .
Nibelheim safe combination
The combination to the safe in the old Shinra Mansion in Nibelheim that contains the key to enter the basement (and get Vincent) is Right 36, Left 10, Right 59, Right 97.