The best way Ive found is, when adding the entity to the struct inst,
store a pointer to the struct inst in one of the entity skills,
or its "reference" number as it is stored in the "item collector".

I sometimes store a VOIDed pointer to the struct inst in the
"entity.parant" pointer too. Only if not using templates for anything.

That way T_ITEM can directly access ENTITY with T_ITEM->pItemEnt
and ENTITY can directly access T_ITEM with (T_Item*)ENTITY->parent