〜とく・〜どく: do in advance (casual)

Casual form of 〜ておく, meaning to do something beforehand.

Te-form 〜て → 〜とく, 〜で → 〜どく: 買っとく, 読んどく. Used in speech. 〜といて is the te-form, and the polite is 〜ておきます. Used in conversation to say you prepared something for later.