You could make an excel(/csv) import, database import, or just create your masterdata through a microflow in the after startup.
Check the appstore for some modules you can use.
What kind of data are we talking about and how much of it is there?
You can configure your app to use a postgreSQL database and manage it with pgAdmin if you're used to working with those programs.
Or install the Excel importer module from the app store, that does take some time to setup up but once you've done that it's easy to import data from csv.