What is the first unpleasant event that occurs on the Joads’ journey? What does that event portend about what lies ahead?

Even early in the journey the Joads suffer a tragic loss, if one less significant than an actual family member. The family dog becomes the first victim on the journey. Its early demise, dying before the Joads even reach the Oklahoma border, foreshadows further losses that the family may suffer like the death of grampa soon afterwards.