It means the same thing as "you're ready to go." You have everything you need. You don't need anything more. "I'm going to travel to try to see the solar eclipse." "Do you have everything you need? "A map showing the path of totality?" "Check." "A hotel reservation for a place that's within that path?" "Check." "Dark eclipse glasses?" "Check." "You're good to go."

Yep, it means 'you're all set.' It means that whatever problem or hold-up is resolved.

It doesn’t imply that you had a problem. It just means you’re ready.

It means ready to leave or to start doing something. The other two answers are good explanations