Reader question: In this – Random thoughts and whatnot – what's "whatnot"?

My comments:

Random thoughts and things like that.

"Whatnot" means other things of the same type that you have already mentioned without actually naming them. Always preceded with an "and". "And whatnot" is similar to:

 and so on (meaning you could go on, without actually attempting to do so) ,
 and so forth (same as "so on"),
 so on and so forth (used in speech, especially perhaps when you have more time than you have to say),
 and such (similar things)
 and such like (same as "and such")
 et cetera (etc. for short, from Latin),
 etc etc (used when even you yourself are bored by the list you're giving),
 ad infinitum (also from Latin, meaning going on and on without ever ending).
And, of course, ad nauseam.

Never mind the last, here are examples:

 and so on (Bleak House, Charles Dickens):
Equity sends questions to law, law sends questions back to equity; law finds it can't do this, equity finds it can't do that; neither can so much as say it can't do anything, without this solicitor instructing and this counsel appearing for A, and that solicitor instructing and that counsel appearing for B; and so on through the whole alphabet, like the history of the apple pie. And thus, through years and years, and lives and lives, everything goes on, constantly beginning over and over again, and nothing ever ends.

 and so forth (Emma, Jane Austin):
"He and Mrs. Weston were both dreadfully desponding. 'How could he contrive to come? And how could it be supposed that his uncle and aunt would spare him again?' and so forth – I always felt that something would happen in our favour; and so it has, you see. I have observed, Mrs. Elton, in the course of my life, that if things are going untowardly one month, they are sure to mend the next."

 so on and so forth (urbandictionary.com):
And so on and so forth. etc...

We played ball, swam in the river, shelled oysters, yada yada yada, and then went home.

 and such (stovesandsuch.com):
Stoves and such

Specializes in wood, gas and pellet stoves, inserts and fireplaces.

 and such like (Don Quixote, Miguel De Cervantes Saavedra):
To which Don Quixote replied, "As all these things and such like occurrences are out of the ordinary course of nature, it is no wonder that Sancho says what he does; for my own part I can only say that I did not uncover my eyes either above or below, nor did I see sky or earth or sea or shore. It is true I felt that I was passing through the region of the air, and even that I touched that of fire; but that we passed farther I cannot believe; for the region of fire being between the heaven of the moon and the last region of the air, we could not have reached that heaven where the seven goats Sancho speaks of are without being burned; and as we were not burned, either Sancho is lying or Sancho is dreaming."

 et cetera (Dombey and Son, Charles Dickens):
"Dear Uncle," said the boy, affecting to make light of it, while the tears stood in his eyes, "for the honour you have done me,et cetera, et cetera. I shall now beg to propose Mr Solomon Gills with three times three and one cheer more. Hurrah! and you'll return thanks, Uncle, when we drink the last bottle together; won't you?"

 etc etc (Longman Dictionary of Contemporary English):
The letter says pay at once, they've reminded us beforeetc etc.

 ad infinitum (The Wisdom of Insecurity, Alan Watts):
In the strictest sense, we cannot actually think about life and reality at all, because this would have to include thinking about thinking, thinking about thinking about thinking, and so *ad infinitum*. One can only attempt a rational, descriptive philosophy of the universe on the assumption that one is totally separate from it. But if you and your thoughts are part of this universe, you cannot stand outside them to describe them. This is why all philosophical and theological systems must ultimately fall apart. To "know" reality you cannot stand outside and define it; you must enter into it, be it, and feel it.