Korean people like using this expresion "언제 밥 한번 먹어요" which literally means "Let's have a meal sometime" when they say good-bye.
The actual meaning of it is "Let's hang out sometime" or "Let's meet up soon". It's kind of saying fare-well.
Since korean people think having a meal toghether is the way they get intimate,
they show that they want to become a friend by saying this.
So it's normally used between two people who just got to know
or acquaintaces who didn't have a chance to be closer.
Also, it can be used between two close people who haven't seen each other for ages.
And, some cases, people just say it (even if they don't really intend to) as a good-bye.
A: 만나서 반가웠어요.
It was nice meeting you.
B: 네, 저도요. 언제 밥 한번 먹어요.
So was I. Let's have a meal toghether sometime.
A: 네, 좋아요. 다음에 봐요.
Sounds good. See you soon.
B: 네, 조심히 가세요.