Explanation
Express doing something in advance or for future convenience (casual form of ～ておく).
Formation
Verb-て form + とく (e.g., 食べておく→食べとく, 読んでおく→読んどく)
Detailed explanation
The ～とく grammar point (from ～ておく) is used to express doing something in advance or preparing for something. It implies you're performing an action now to avoid inconvenience later. It is a casual, colloquial contraction of ～ておく.
Examples
Yoru osoku naru kara, konban no gohan wo tsukutoku.
Since it will be late tonight, I'll prepare dinner in advance.
Kasa ga hitsuyou kamoshirenai node, motte oku.
I might need an umbrella, so I'll bring one along (just in case).
Shiken ga chikai kara, ima kara benkyou shitokou.
The exam is coming up, so I'll start studying now.
Ashita wa isogashii node, sentaku wo shitoku.
Since I'll be busy tomorrow, I'll do the laundry in advance.
Practice
Grammar content sourced from hanabira.org.