I didn't steal it, it's a free "public Domain" 3D asset. I was looking for one and found it. You'd be surprised what we could find that are Clip Studio Paint compatible.
This one is in .glb format which means it contains the texture.
This image is only an example of how to make the carton milk interact with a model (model not included)
Lock (attach) the "carton milk" under the right hand in the sub tool detail of the model and you don't have to worry about moving the milk carton again while moving the arm. The carton will follow as the arm moves.


Material