There is a chance I misplaced some of the calls in that list. A query won't work after a THEN, for example. But the list I got that from didn't define queries/calls (actions), so it's kind of trial and error.
This lead me to the solution.
Indeed, "ListGet" is only available in the IF / CHECK. So now I ended up with a bit of akward code. I'm using the OnInit event to populate my list in the THEN action.
Within the IF of my OnUseItem event, I use the ListGet query to get one of the elements.
Not pretty but it works.