What Goes on A Great Thank You Page?

Was having this discussion in Telegram and decided to bring it here for consideration, since we're all marketers.

The question: What do you think belongs on a perfect thank you page that someone is sent to after entering their email on your lead capture page?

Me personally I think a thank you page should have explicit instructions on what to do next. I even went so far as to write an article on how to whitelist within gmail and had that as part of my main email intro so people know to whitelist my stuff from the get-go.

What's your take?