Safecracker
Crack all safes.

Each business (plus the New York Federal building, each bank, and the Florida airport) and compound (except for the Corleone compound) has a safe somewhere inside. Youll need to have a Safecracker with you to be able to break into them. You can do these after the story is completed, and you wont have any interference from the other families while youre trying to break into them.