I'm making a miniature cave set for a short film? How can I make the cave look realistic?

I am not sure that this will help but you mentioned the materials you have left. If you have someone really good, make some bones. Also its winter, put down snow. Find twigs that could resemble trees and the smallest of the twigs spread them around for the branches that fell off the tree when it fell. The bones could be put by the tree that fell on one of the Hessian's. Sorry but that is all that comes to mind at this time.