Yesterday, after our 2nd picnic in the backyard we still had some time to kill before nap so Mommy came up with the game "Nature Hike."
The object of the game is to walk around the yard and collect as many different pieces of nature as you can. Of course, each time you find something you need to bring it back to the blanket immediately (thus a lot of kid-tiring back and forth running exercise!) You could omit that step if you aren't trying to exhaust your child.
When we were done we had pine cones, rocks, sticks, bark, flowers, dried leaves, fresh leaves, grass, black walnuts and god knows what else. We looked at it all and sorted it and played with it. I tried to think of some craft to do with it, but really, the act of collecting, touching and discussing it all was enough!