I have found that the best outside toys are recycled food containers. They love to play with any type of cleaned-out bottle or container. I love it because once they're broken we can just toss it and get something else. This old syrup bottle Gabe has works great in the pool as a squirt bottle.
When the rain brought everyone inside, I let them get out the craft stuff to kill some time. We haven't done much crafting over the summer since I encourage them to be outside as much as possible and we've done a good bit of traveling.
I assisted in the making of these two little people and then left Gabe and Mya to come up with their own ideas which is what they really enjoy doing.