Look out for pumice and coal while walking along the beach.
If you find a piece of pumice, pick it up and you will feel how light it is!
Pumice is formed when volcanoes erupt explosively. It is so light because when the rock formed it was full of gas. This is because it formed so quickly. The gas has since escaped, leaving all of these little holes.
The coal pieces you might find have likely fallen off ships and washed ashore.
You might also see little pieces of broken coral along the shore.