뭘 이런 거까지 준비했어요? literaly means
What did you prepare up to such a thing?
It is an idomatic expression. it means
"Why did you take the trouble to carry such a stuff?"
Actually, "Thanks for your present!"
뭘 is colloquial form of 무엇을(of what)
뭐 is colloquial form of 무엇(what)
ㄹ(을) is a accusative particle
이런 is colloquial form of 이러한(such, like this)
거까지 is colloquial form of 것까지 (up to thing)
거 is colloquial form of 것(thing,stuff)
까지 means "up to, until"