This may not fall under sisterhood, but it is fun. Get all the girls together and find a pot (any pot, just small) and a pot holder, but don't let anyone know what you've got. The put everyone in a circle and ask for some volunteers. Pick out three or four and separate them. Then give the pot to someone left sitting in the circle and get them to put it behind their back. Bring the one of the volunteers in and tell them that they have a challenge. They have to hug the "pot holder" without using their hands. Then drop the pot holder in the middle of the circle and watch the girls contort. It's hilarious (and the volunteers have a blast too). Eventually, let the real potholder start banging on the floor with the pot. Usually, the volunteer will be so concentrated that they won't get it. But when they do, it is sooooo funny!
Another game is where you get some other volunteers. Then you set out a chair and tell all the girls watching to imagine that the volunteers are on the toilet. Then, tell the girls that we are playing charades and that they have specific things to act out. Examples - Roller Coaster, Who Wants to Be a Millionaire hot seat, in a scary movie with a boyfriend, and I'm sure that you can come up with some others. Make sure you don't tell the watchers what they are acting out, but tell them to play dumb. You'll have tons of fun.
We also do stuff like horseback riding, and a girly night. Then, we all spend the night at the house and wear PJ's and do hair and makeup. I know it sounds silly, but we usually end up with funny makeup, and later we usually get all emotional and really bond. I suggest that you do things like going to Steak n Shake after chapter, or rent a movie and watch it at the house, or go knocking on the frat houses and sing for them. You can come up with lots of stuff!
Hope this really long post helps.
Allie