LOL a 90's theme party sounds like fun!!
Acid washed jeans, lumberjack/plaid print, blazers, big boxy tees tucked into pants, baby doll dresses, vests, knee high socks, and mary janes used to be hot 90's fashion.
I would do a grungeish look. I'm thinking a plaid shirt, open in the front, a tank top that shows you stomach underneath. Paired with some looser jeans. And of course a full face of makeup with dark lips and lipliner.