Let's enjoy Japanese: Do it up!

*Updated - apparently ～とく is equivalent to ~ておく。See below for further explanation.

This one is a little wobbly, so bear with me. Those of you with extensive Japanese experience please feel free to comment on this one.

今回は、この文法はちょっと不確かだから・・・我慢してください。日本語上手い方は、良かったら、ｺﾒﾝﾄしてくださいね。

So there's someone I've been talking to a lot recently who sometimes uses a grammar pattern I had never noticed before. It seems to add a degree of enthusiasm to a verb. I am referring to ~とく. To put this bad boy to use, you take the ~て form stem of a verb and add とく. And that seems to be it.

If I understand this correctly, しとく, therefore, would mean something along the lines of "Do it up." It seems difficult to translate into English with most verbs.

Example: わぁ、疲れた！今夜寝とくよ！

"Man, I'm beat! Tonight I'm gonna sleep like a champ!"

最近のよく話してる友達はこの文法を時々使うけど、僕はこの前に例の文法に気がつかなかったんだ。例の文法は動詞と付くと、なんか熱狂になると思う。これは「~とく」なんだ。

英語にちょっと訳しにくいけど・・・

Anyway, I have never come across this grammar pattern in any textbooks or online resources, but I'm sure it must be somewhere. What little I do know I learned from a friend of mine who was kind enough to try and explain. So again, if anyone has any corrections or additional thoughts, please leave a comment. I'd be interested to learn more about this form.

とにかく、この文法は、僕は教科書とかインタネットで読んだことないが確かにどこか習えるね。だから、ｺﾒﾝﾄや考えあったら、コメントしといてくれね。この文法についてもっと習いたい。英語でも日本語でもいいよ！

*Update: A clarification from Bryce -

「〜とく」is just a shortened version of 「〜ておく」(to do something in advance or in anticipation of something).

(slang) 明後日はテストだから勉強しとこう。
＝
(proper Japanese) 明後日はテストですので勉強しておきましょう。

例えば：
「おれ、言っとくけどさ、一杯やったら帰るつもりだ」
"Just to let you know, I'm planning to call it a night after I have one drink."