While scene writing, or any kind of writing, at times you’ll know you need to write something, but nothing comes to mind. We don’t want to pause writing mid-stream, and we don’t just want to leave a blank. Enter: TK. From Wikipedia —

“To come” is a printing and journalism reference, commonly abbreviated to “TK”. It is used to signify that additional material will be added at a later date.

I use this all over my first draft. If there’s an emotional reaction that I know I need but the tone isn’t coming to mind, I’ll write TK_his_heart_beat or TK_he_smiled. If suddenly I discover I need to research what the environment looks like, I’ll add TK_setting. Or maybe a new character showed up while writing and you don’t want to name him yet, TK_name. And on and on. Each of these frees up the mind to stay in the writing headspace, while still looking out for my future self.