Last time we went to the canyon, we pressed leaves into our copy of The Book of Virtues. Weeks later, the leaves are still vibrant and perfect.
You might remember that last year, we took fall leaves and put them up in the window with contact paper. We'll probably be doing that again. I loved the look and feel of it. For details, see last year's post.
PS. If you are interested in a very LDS post about teaching your children about the Spirit, you can find my post at Latter-day Homeschooling.