Can't add item to entity's inventory without open GUI

I want to have an entity that moves around collect wood, and gets planks from every block it breaks. I am using the trigger [on entity tick update], which means I can only use the dependencies [world], [entity], [x]. [y] and [z]. So that means I can't use most of the item procedures, and I can only use the GUI procedures. The problem with that though, is that all of those require an open GUI. I want the entity to work by itself. What should I do?