Have a good one!

What in the world does this mean?

I have noticed this odd saying when one is ending a conversation or lack of conversation.

Good one what?

Typically refers to a good day.

I just helped someone here at the church building jump their car and all I could say was, "Have a good one."

Thanks! (My car battery is dead, but I am going to have a good one.)

I need to come up with a more authentic ending to a conversation.