How do I give a new user the same permissions to individual files as an existing user?

I have a user that is leaving the organization. We need to give the incoming replacement user permissions to all the files the outgoing user had.

I can easily identify the SharePoint groups the outgoing user belongs to and grant the incoming person access to those groups. This includes the personal site files and most team site files.

However, there are some files that the outgoing user has direct access to (item-level permissions), rather than through a group. How do I identify these files?