How do you change the "Material" of the items in ItemsAdder?

I have bought some "packs" from EliteCreatures and added them to my ItemsAdder plugin. They allow me to go in and change the Material to whatever item in the base game I want. Ex. Beer was originally a feather and was not eatable, but I wanted it to give nausea and hurt people but not kill them. Well Pufferfish meet all those requirements, I just had to change the material that it covered with the new skin to Material: PUFFERFISH. And it now looks like a beer, but functions as a Pufferfish. I want to do this same things with the base ItemsAdder items. Where do I find the base ItemsAdder items to switch the materials like I did with the Packs from EliteCreatures?