Data
Keep data in your workspace for your flows: rows in tables, settings in schemas and documents in files, each kept apart for Test and Prod.
All three are under Storage in the sidebar.
Store data in a table
Make a table with typed columns in Test, add rows, and let your flows insert, find and change rows with the Tables nodes. Put it on Prod when it is ready.
Keep settings in a schema
Keep a JSON document, such as shipping rates, that several flows read: make it in Test, change it in its editor, and copy it to Prod.
Store a file
Upload a file, such as a price list or a template, to your workspace, keep it in a folder, and read it in a flow. Each file belongs to one environment.