Japanese by Example
Learning through examples in manga

Reaching out before shopping with 〜ておく

ご注文はうさぎですか? » Volume 1 » Page 78

Since Cocoa will be making stew for dinner, Chino decides to communicate in advance to get ingredients other than carrots.

チノ:
「にんじん以外(いがい)(つた)えておこう

Here, おく is is modified to the volitional (showing intent to do) おこう. “I will send a message …”