Our chapter does things like sister speed dating where we have two rows of chairs and you "speed date" with the sister across from you. We're given a list of random questions that we ask each other and talk about for like three minutes and then we switch. Sisters in one row of chairs moves to the left, and the sisters in the other row of chairs stays in the same place but passes their questions list to the right. It's a lot of fun and it's free
We also do things like movie nights, ice skating, and sisterhood dinners. These are always a hit, too. One of my favorite things is our friendship journal. We have a journal that our VPCD started and she chose a sister that isn't in her "clique" and then wrote to that sister telling her why she was a great addition to our chapter, why she's glad she's gotten to know her, etc. And each week at meeting we pass the friendship journal to a new sister. It's a really great way to show each other that you appreciate one another even if you aren't best friends.
We've done other things as well, like building a Habitat for Humanity house, giant sisterhood shopping sprees right before formals for dresses, and a chapter-wide secret santa exchange. Hope this helps!