Picnics at the park behind our house, it can be P&J and Capri Suns, but with the playground and all the grass to play on it's fun!
Homemade playdough, there's so many different variations, we like the "kool-aid" one the best.
http://fun.familyeducation.com/sculpting/recipes/37040.html
Movie marathons on the DVD, we pick a theme and run with it.
Days at the fountains at a park across town, we take our lunch and stay cool, the kids get tired and rest when we get home.
Sidewalk chalk, they have had a blast decorating the driveway, even the 27 month old.
Reading.
Extra tae kwon do classes, they don't charge any more and encourage it!
Free movie nights near the beach : )