Thanks for the additional comments.
I have at this point decided to include bones only when it's a complete skeleton - so Betty, the mammoth, and the fish skeleton.
I am going to leave the troll out for now. I will leave it open to possible future inclusion if I feel like it.
I have included the 123 snail and 123 dino, and do intend to include the swan boat. My thought process is that if it looks so much like an animal that a stranger who didn't know it was supposed to be a boat/rocking ride/whatever would go looking for it then it should be included. We know it's a swan boat, but if you just had the swan part and weren't that familiar with Playmobil lines would you think swan first or boat? I think it would as likely be swan, so included.
Thanks for everyone's comments on this, and feel free to keep discussing. It's all been helpful in working out my criteria and thought processes.