If you go, bring your lunch.
If you go, take your lunch.
Which sentence is correct?
Both are understandable, but there is a difference in meaning based on the speaker's frame of reference.
If the speaker is not going with you, then "If you go, take your lunch" is most natural.
If the speaker is at the destination already, then they sound most natural saying "If you come, bring your lunch"
"If you go, bring your lunch" is an interesting case.
This has both the person moving away from the speaker, and the lunch coming towards the speaker. This seems like a contradiction, but has a few uses!
If the speaker:
Then they might say "if you go, bring your lunch".
For example, you and your friends are all meeting at a park and your friend calls you on the phone before leaving.
Another case for this usage is if the speaker is empathizing strongly with you, like perhaps a parent to their child - especially if there is a sense of teaching or admonishing.