Contrary to these other terrible definitions, it literally just means "and other, similar things." Or "whatever else."
Very common and simple to understand.
Synonyms for and Whatnot
On this page, you will find 30 slang terms related to and whatnot. Some of the top words include: Swingman, what the shit, Snostrebor, srcabumpous, whut, and 25 more.