Several years back when I was a nanny, I came up with the idea that I would let the kids pick one thing a day that they could do. (Whether it was crafts, going to the zoo, or baking we made sure to do that one thing.) It made the day easier because they were much calmer knowing that they would get to do one thing of their choosing during the day.
So I took that idea and mixed it with Ellie's "Date Lottery" and came up with the "Summer Lotto." Each morning the kids get to pick one item out of a whole slew of things to do. They don't know what they are going to pick so it adds a fun element of surprise.
Some of the activities are;
Build a Fort
Summer Scavenger Hunt
Sidewalk Chalk Art Show
Backyard Camp Out
Download the Summer Lotto PDF to get all the ideas! You can simply cut out the paper strips and stick them in a bowl, a hat, a jar, or whatever you have handy and let the kids pick out one thing a day.
Make sure you have plenty of water balloons on hand and be prepared for some fun!