The first option sounds natural to my American English ear:)

Number one is more natural: I am probably talking about lunch at home on my own. As Jonathan suggests, number two is more formal, so it would not be used in this situation of a husband talking to his wife - about leftovers... "Tomorrow's lunch" would most likely be used in the context of an organised group lunch meeting, e.g. a group of work colleagues eating lunch together or a business lunch. e.g. We've decided to move the venue of tomorrow's lunch to a cheaper restaurant due to budget limitations. Obviously, in such a context, the participants would not be eating leftovers! 😉

use 1 2 isn't bad but it's kinda more formal.

Either is fine to me ( British English) , but will there be anything left for your wife's lunch ??

How about below one, is it appropriate? I can eat the leftovers on tomorrow lunch