I drew a grid on a piece of calico and wrote the the letters of the alphabet in every square (you could use paper, card or any material). I then used anything from nature that I could write the alphabet on. Once you start looking your realise that there are loads of resources right at your fingertips. All of these nuts and leaves were found on the ground at the park across the road from my house. Don't you just love a resource that costs nothing! The gum nuts have been used before on the blog "Bringing Nature Inside".
See what natural resources you can find in your local area.