For storing country-specific data such as price book details and image URLs for a country flag, particularly in a multi-country Salesforce B2C Commerce implementation, the most effective approach is to use a replicable, site-specific Custom Object. Custom Objects in B2C Commerce are ideal for storing structured data that can vary from one site to another and need to be replicated across different environments from staging to production. This method allows developers to maintain a consistent data structure while being able to tailor the data content to specific country requirements without impacting the global data model. Additionally, Custom Objects can be managed through Business Manager and replicated across environments, making them suitable for both development and production settings.