I've got an average experience with OPA but inferring entities is not one of my strong sides. I'd assume that I'd have to create a child entity 'the packed item' (e.g.) and a rule that states that 'the debrief item is a member of the packed item if the debrief item is in the box' - or something like that? 

I was already afraid this was the case, even though the documentation states that I should name the relationship to use it in BI Publisher later on... guess a functionality that doesn't exist yet?