I printed the picture cards off a while ago from Sparklebox and use them time and time again for different activities. Ideally you would add real leaves that you can find with the children but I have to say that I love these that I found in the works for children to sort into colours or use to make pictures with.
I added some conkers from the nearby trees where I live that have them in abundance, a large pine cone that a friend gave me (you can find lots of these too at this time of the year when you go out for walks in the woods etc) and a squirrel and hedgehog finger puppet.
There are so many other items that you could add including some acorns, apples as its harvest time and maybe a pumpkin too.
Have fun putting yours together. There are so many opportunities with this to develop early language skills, early number skills and to have fun together including leaf rubbings.