Graduation Ideas?

We're back from our vacation (pix and update soon), but now, reality is setting in.  I will have two graduates in less than a month!  We have 18 school days left.  I need ideas!  I want to have some kind of celebration, but nothing fancy or expensive.  We did a surprise party for their 16th birthday two years ago (yes, two kids, one birthday, aka-twins).  I don't want to do anything like that, but I want to celebrate with them.  I think I might need to have it the weekend before graduation, but I digress.  Please, if anyone has any ideas for something simple that all ages (family and friends) would enjoy, let me know!