T.O.
My daughter has some really interesting "days" marked on the summer calendar. So far she's had "outdoor games day", "international food day" . "lazy day", "breakfast food day" and some others I can't remember right now.
She makes these up and then does things around the theme for the whole day.
Int'l Food Day we tried to make stuff to eat that was from a different country each meal. It can be really simple and you have the internet so you can get ideas and even videos on line to show you how to make it. You can get lists of games to play outdoors for game day etc.
Anyway, let them make up the days (maybe they each get to pick one day a week) and put them on the calendar and see what you can do with that. I put "the day" on the dry erase board and add what I can to it, but I do work so the kids have to take carry out the events on their own for the most part.
Good luck.