A old skool Yorkshire phrase. Meaning you, someone or something is fine. Something is in good condition or is pretty perfect for what you need.
Q: Do you have a bad hangover after last night pal?
A: Nah mate, I'm reyt as a bobbin.
Or
Q: Does that jacket I bought for you fit you? Do you like it?
A: Yeah, it's reyt as a bobbin thanks.