Welcome to the forums @"Fantasy Haven"!
Godot doesn't have bundled packages like the UnityPackage file used in Unity. Instead, most assets are just the source files zipped and uploaded, so they can be uncompressed and then placed into a Godot project directly. The Godot editor can also unzip projects that have been put into zips as well.
So I think all you would need to do is take the assets you want to offer in a package and zip them, then upload them to Itch.IO! :smile: