Pretty much anything that's been certified as genuine, this means coins, tokens, paper notes, stamps and even some artwork from the first couple of years.
The certifications will be very important as anything that goes up in value will eventually be copied/faked. Dated items will demand a premium as well as anything
first generation.
I agree. Also, The actual grade of the item will be more important at some point. The value of a MS62 1 Cas and a MS 66+ could be a big value difference.