How about a talent show!! Have parnets and kids do whatever. Sing, tell a joke, read a poem, anything really. You don't have to have a judge. Everyone can show sometime or another. Our kids love this. Parents and grandparnets love it to. Have each parent/family bring a plate of cookies or something to drink and have a party after.
Try a movie night.The kids use their sleeping bags or blankets to sit on in the gym. Videos are cheap to rent or borrow. Sell popcorn/pop for .50. Even if it gets snowed out, you won't be out much money.