The obvious and the not so obvious (3rd on the list) which is used really often!
Να’σαι καλά! = να είσαι καλά =
Literally means “I wish you to be well” something like “take care”
Να’στε καλά! = να είστε καλά! = formal way or addressing two or more people.
Remember to put the apostrophe after «να»

Επίσης = you too (the same to you) so in cases like «καλό ταξίδι» unless you know the other person is leaving after a while, otherwise keep it for public holidays, as an answer to «χρόνια πολλά», or «καλή εβδομάδα» and «καλό μήνα».

If music and especially songs help you memorize vocabulary, expressions and learn in general easier, which is so true, you can find more than one songs on the internet with the title «να’σαι καλά» like the one I’m suggesting here from a singer called Ελεωνόρα Μελέτη.