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) Depends entirely on how long the locals put up with my uselessness. I might just die of diarrhea too, considering I have nil immunity to local germs and there’s no sanitation.
B) My clothes are now the finest textiles on earth, and I carry a multitool. In some ways, it might actually be better if I was naked and pitiful. Maybe they’ll take me seriously long enough that I can build something for them, or find a kind of type clerical work that they actually need. Or, maybe they immediately rob me, kill me and dispose of the body before the other pale giants show up.
C) Hmm, more interesting in a sense, although in many ways it’s just a bigger version of the clothes problem. I couldn’t really defend my house if they decide not to respect my ownership (and why would they? it was feudal times). And a whole building appearing from thing air is pretty much proof magic is afoot, which can go multiple ways.
If they decide to humour me, I could do serious work for them pretty much immediately. These are people who still do a lot of things with stone tools. I can also introduce them to some new crops.
The diarrhea is going to be one of the biggest challenges. The differences is food, parasite/microbiota challenges… dehydration and acclimating to the local food supply are going to present problems.
You’ll probably be killed for washing your hands before eating or something.
Eh. Some traditional cultures do that anyway. I highly doubt they’d freak out over it, let alone to the point of violence.
They might think you’re weird, and you’re probably going to have to gather your own washing water, though. And if they’re doing clean hand/dirty hand you should also respect it.