What kind of treasure was in the bundle that the Bhil robbers tried to steal from Kashiram?

The premise of your question is based on the robbers' misunderstanding. The small bundle they tried to steal from Kashiram did not contain any treasure. As Chapter 0 explains, the thieves only thought there was treasure inside. In reality, the bundle was filled with powdered sugar. Kashiram carried this sugar because he had been advised by a saint named Janakidas Baba to feed it to ants. This act of charity was so important to him that the bundle was very dear to him, and he fought the robbers to protect it.