One of the popular (and delightfully easy) annual activities of our club is Family Game Night. It's simple. Families each bring a board game they like. We set them up and people wander around, sharing and teaching games. It's good social time.
Muffins with Mom-- early morning in May with a photo opp... same with donuts with dad in FEb- close to Valentines day, Movie Night, Cookies and Cocoa with Santa, Breakfast with the Bunny (pancakes made by dads), Bingo Fun, Science Night is one of the best though-- no fee to come and the kids love it--The science teacher and teachers throughout the school put the event on-- the kids come in and walk around with their parents and participate in different experiments-- all hands-on at different stations-- no food-- but the last experiment is with a smarties- so most of the kids got to eat some. Kids love this event and asked every year when it will be.
In addition to many of the great ideas already here, our school has done a bunch of others that we have found to be particularly fun. I am in New Jersey, so you'll have to modify for Massachusetts. Our fourth grade students do something called NJ cake day. Each of the students in the fourth grade is asked to provide either a cake in the shape of one of our 21 counties or a container of icing. The cakes are cut using a template provided by the teachers. At the beginning of the day, the students put each of the counties together with different colors of icing and then use decorations to point out spots of agriculture, landmarks, etc. Then there is an assembly with all of the parents and the students do a presentation on New Jersey, sing a song that names all the counties, and then everyone enjoys a big piece of NJ cake!
We do a Mother's Day presentation in the second grade where the kids make the moms (grandmas, aunts, significant female figure) a gift for presentation, they sing songs and do some simple skits. This is huge hit with the moms and they usually wind up crying at the end.
Some other ideas:
Family bunco night
Thanksgiving feast
Family fun Day (we hire carnival rides and games and give out Oriental Trading type prizes) and all the kids get to go free
Last day of school pizza party for all classes (sponsored by the HSA)
Pasta Night (all volunteer cooked and mostly donated meatballs, salad, bread, etc. pretty much all we pay for is the pasta and sauce)
If you google Dr. Seuss there is a website that will give you ideas on what to do. We had several carnival type games (low key though not like a real carnival) a hat building table, couple of crafts, a poster contest (oh the places you'll go with Dr. Seuss) a big birthday cake and we all sang Happy Birthday and cut the cake (served it too) a sampling station for green eggs and ham, and we ended the evening with a round the rocking chair reading of one of Dr. Seuss's book. We had one member actually pull the whole thing together this year. It was a lot of fun and the parents really liked having an event indoors where the children could do something in the March weather.