You may not keep these words in your kit, but they could be a cute addition. Not cute like a kitty, though – these are not words to pet, even if they could be petty words. They are better suited to a kettle of fish, and not a fine one either.
I have an instant association with ket, but it’s not an English one. It’s from a set of lessons in Breton, which is a Celtic language spoken in Brittany, France. (If Breton and Brittany sound like Britain, it’s not a coincidence: the people in question were, a long time ago, Britons, but they were driven across the channel by the Anglo-Saxon invaders.) The dialogue includes this classic line, which you can even hear spoken on the page at Kevarker.org: “Ac’h ! N’eo ket gwin !” Which means “Ecchh! That’s not wine!” The ket is the second half of a two-part negator (French has ne…pas and Breton has ne…ket). So it’s negative. And in the dialogue in question, it’s rather disgusted.
That is not where the English ket comes from. Rather, you should turn to Scandinavian languages: Swedish kött, Icelandic kjöt, Faroese kjøt, Norwegian kjøtt, Danish kjød or kød. They’re all from the same origin as ket. In those languages, it refers to flesh or meat. But in English, it’s gone downhill a bit. It’s raw flesh, thence carrion, and rotten meat, and by extension from that trash or rubbish. And ketty means… let me quote the Oxford English Dictionary for that: “Having bad flesh; carrion-like; rotten, foul, nasty; worthless. Of soil: Soft, peaty.” So… disgusting.
It’s kind of a pity, isn’t it? A cute word like this one, so crisp, even a bit rakish. Its overtones are not nasty: kit, cat, cot, cought, cut, pet, kitty, jetty, cutty, kept, kex… Why would you want to cut this out of your kit? Other than the fact no one will understand it, of course. But if you want to slip in some petty cutting remark, it’s there for recourse. “This is a fine ket of beef you’ve served.” “Oh, there’s your little ketty cat.” And it’s less crude than some other ***t and ***tty words.