I come from a smaller organization, but communication is the key to success! Making cupcakes is not a fun time, we found meeting with organizations of the opposite sex, often make for a fun time. You can do some type of crafts event, like make greek t-shirts ( for up coming rush) and have a competition. You don't have to bring liquor in the equation either, just enjoy the company. If there is a parade coming up you guys can build a float or do something fun like play touch or if your TUFF TACKLE FOOTBALL! ( Not real tackle just some contact (:
With a sorority that large you probably have clicks, you should always try to pair brothers or sisters who don't reall hang out that much outside the house, and that always makes things interesting. Do a safe scavenger hunt, were you have to get funny things and funny pictures!
I am just trying to keep it PG LOL!