I would definitely go with the rolled up jeans (preferably stone washed), high top gym shoe's, and a baggy t-shirt that you can either tie in a knot or fold it into something like the girl in the back with the purple shirt has. I forgot what those plastic things are called.
I know this is more of 80's wear, but I just wanted to get the idea of the plastic holder in the knotted shirt.
Also, you could always go with bib overalls...those were popular in the 90's.