I think all the supernatural elements of Yellowjackets can actually be explained as the spirits of the dead interfering either to help or punish.
The bear is Laura Lee taking care of her friends. The snow on Jackie's body is her allowing herself to be consumed if it means her friends survive. Javi survived on his own for so long because his dad was looking out for him.
The things that aren't directly linked to characters we know could equally be other spirits that died in the wilderness - the others that died in the plane crash, the man in the cabin, the owners of the survival equipment Ben found.