Items that go into the inventory should go into the bag where the same item is already present.
Often, I have to sort my bags because ore and other chunks ended up in all bags. Or I have to fill up bags I don't want stuff to end up in.
This could either be fixed by allowing to take a part of a stack from a slot (see other idea), or by making items group automatically. This way a few bags could be 'initialized' with the stuff that should end up there.