There are a few places, where you can extensively edit Minecraft items. They include:
Generator item
Generated item
Recipes file
Custom drops item
What can I set?
Using extended item configuration its possible to set:
Amount
Name
Lore
Custom NBT
Custom head via material: "customhead:<base64>"
Custom Model Data
Simple vs extended configuration
At any place, where item is about to be configured there are two options possible to achieve that. Simple configuration saves space and is perfect, where you only want to set item material. Extended configuration on the other hand gives you the opportunity to freely customise ItemStack.
Simple configuration saves space and is perfect, where you only want to set item material.
...:
item: STONE
Extended configuration on the other hand gives you the opportunity to freely customise ItemStack.