Strawberry smoothies.
When I was a freshman, there were 4 NPC sororities and a brand-new local on campus. The local held their rush after NPC FR ended. I went through FR, and none of the NPCs felt "right" for me ... so I checked out the local. Their first rush event was a mocktail hour, where they offered 4 or 5 different mocktails, including strawberry smoothies (I think I had 3 over the 2-hour period).
Diet Coke also holds a slight connection to my sorority for me. During my junior year, I was in charge of bid day. During an early round, I spoke with a PNM who mentioned to me that she was diabetic - the only thing she could drink at parties was water, and she couldn't eat most of the hors d'oeuvres offered to PNMs. When I saw her name on our pref invite list, I alerted the day chair for pref to ensure she would have something besides water to drink (we usually do sparkling cider but I think she got Perrier) and I made damn sure there was a Diet Coke for her on bid day. She became my little.