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Aside from saying thank you and offering any additional materials if necessary, what else should be in a post-interview thank you email?

You don't even have to send one at all. But if you do, nothing more than what you already mentioned is necessary. There are like a million threads on this, I'm sure there's more info if you are really curious.

Edit: If you really hit it off with the interviewer, maybe include very brief sentence that mentions a good conversation you had or something.