@Glenn Maxwell
Which version of SharePoint are you using? What types of data do you want to copy from a site to another site?
Here’re some methods for you to copy data:
1.Save list/library as template.
Manage list templates
2.Save site as template.
Save, download, and upload a SharePoint site as a template
3.PowerShell.
SharePoint Online: Copy files between site collections using PowerShell
SharePoint Online: Copy list or document library to another site using PnP PowerShell
Copy list items from one site to another with versions using PowerShell
5.Move to/Copy to action in the SharePoint Online.
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