The dinosaur’s last meal in Stardew Valley is a Solar Essence. You need to bring it to the sand dragon skeleton in the Calico Desert as part of the Qi quest chain.

How to do it

  • Go to the dragon skeleton just north of Sandy’s Oasis in the desert.
  • Hold a Solar Essence in your inventory.
  • Interact with the skull to complete the “final meal” step.

What it unlocks

This completes that quest step and leads you to the Club Card, which opens the Casino.

Quick note

Players sometimes guess sunflower, bomb, or other “sun-related” items, but the correct item is Solar Essence.

TL;DR: Give the sand dragon a Solar Essence.