DecorItem data tag in minecraft
Solution 1:
The DecorItem tag is a compound holding item data for the item within the llama's "decoration" slot, highlighted here:
While the decorative appearance on the llama itself requires the item to be any type of carpet, using commands you may insert any item at all into the slot:
/summon minecraft:llama ~ ~1 ~ {Tame:1b,DecorItem:{id:"minecraft:stone",Count:1b}}
