Tom: "We have a big exam today. Are you ready for it?"
Sam: "Yeah, I studied all night. I'm all set."
Kathy (on the phone): "Hey Jane, I'm on my way and I'll be there in about 10 minutes to pick you up.
Jane: "No problem. I'm all set and ready to go."
Meaning: "to be (all) set" is an American idiom that is used to express the meaning of being ready and prepared for something.