First mention of the town "Riverdale" which takes place in the same universe.
The hypothetical that Sabrina gives Harvey is basically that of SHAZAM: a wizard giving a kid super powers.
Hilda Spellman (Lucy Davis) is telling Sabrina (Kiernan Shipka) about how handsome her father was to the point that he could have been a famous actor like Cousin Montgomery. She is referring to Elizabeth Montgomery who starred in the TV series "Bewitched" that ran from 1964-1972. Although she might have been talking about Madison Montgomery from the show American Horror Story: Coven.
The newspaper that aunt Zelda is reading at the kitchen table the morning after the Dark Baptism ceremony, is in Russian. The title on the front page is written in Russian cyrillic letters which transcribes to "Moskovskaya gazeta", which means "The Moscow Gazette".