Wiktionary
eat in
vb. to eat a meal at home.
WordNet
Usage examples of "eat in".
We won't likely eat in the kitchen much after tonight, with Summerset due home tomorrow.
He slept every night, and paused to hunt for berries and fruit to eat in the woods.
Scott arrived and Maureen gave them a few minutes of privacy before asking the boy to keep her company while she got something to eat in the cafeteria.
You can't get a decent bite to eat in my house these days with all the tofu this and rehydrated vegetable that.