A) Nothing, just totally naked
B) What you’re wearing and anything you carry with you (even if you’re not carrying it right now) like a bag
C) What you’re wearing, what you carry with you, and the contents of your home (it will be teleported within a few hundred metres on the surface in an accessible location, but obviously won’t be connected to any services like electricity or water)
A heads up is not gonna save them from their real killers, smallpox, unless you brought it with you and give them a couple centuries to recover population and gain immunity.
I’ll do my part with the locals—wait shit that’s what they did!