If you have or live near an oak tree, there will be an abundance, always, and all you have to do is collect them.
Pick up all the fallen branches and collect them for firewood. They are perfect if you have a fire pit!
Play up the Green Man (wild man of the woods) motif by making leaf covered masks and headdresses.
Eat an apple. No, not an oak apple. A regular, old fashioned, honest to goodness apple. Eat them all year long. They're good for you.
Hug an oak tree. An important thing to remember here is that trees are the lungs of the world, so take care of them..