A.L.
Picnic at the park?
And here's the catch: assign everyone to bring something. (I'm hoping you have a lot of parent support?). Have everyone promise to bring it. That's "responsible for what I say."
When you leave, you can introduce the rule, "Always leave a place cleaner than you found it." Bring a digital camera, for before pictures, and have the girls clean up their things, so that it looks better than when they came (or at least, just as clean!) That's "responsible for what I do."