The gold chain and charms in this picture were reportedly given to Catherine by her sister Pippa. They are an oak leaf, an acorn, and a mushroom. The first two of course come from her dad's coat of arms. Not sure about the mushroom - Prince George??
Before, during much of the tour, Catherine was wearing a Mappin and Webb diamond circle on a chain. I think it has three intertwined circles. It seems to be new, possibly a gift from William after the baby's birth.
Hope this is accurate. The Duchess Kate blog describes her jewelry as she wears things. I expect you are seeing great television coverage of the tour!