Im pretty undecided about what path to take here. The simplest that comes to mind is just adding a field List to the GameObject class where i would store the things contained in it. But would it be elegant and well tought? And would it be good performance wise?(ofc 99.9% of my objects wouldnt have anything stored in them...)

What about deriving a ContainerObject from GameObject? This way only they would have additional fields but then i would have to change many things, my collections of objects would have to become a generic and id have to cast very often into GameObject...