The littles and I spent Wednesday night filling a box with large leaves, vines, and flowers, that we made from materials we had around the house, to send in to Mackenna's class for their next round of dramatic play- centered around the book Afternoon on the Amazon.
I had also found numerous related activities, for the kids to do at center time, in the book Crafts for Kids Who Are WILD About Rainforests - all using supplies you have lying around your house. Unless, unlike like us, you don't have empty toilet paper tubes, construction paper, tissue paper, yarn, glue and scissors lying around your house- then you'll have to buy a few things.
You may also want to pick up a pink sock (Peanut is found sleeping in one in this story) and if you are REAL ambitious- figure out a way to make a canoe for two. I'd probably use just an empty box at home, but I didn't have 5 to send in to school.