Egg, Gold & Faberge
Treasure-laying animals such as golden geese have always been highly prized by the nobility, not just for their wealth but for the possibilities of types of wealth through selective breeding.
This is why monsters like cockatrices and basilisks have become problems in the realm. They are failed, escaped, or abandoned progeny of such endeavours. At worst, disposed of in areas far away from royal property or at best, ill-trained guards of the grounds.
Golden eggs are often laid by "golden geese," so are the size of a human palm and hefty.
A very excellent D&D treasure are Fabregé eggs. There are 52 of them, all ornate, themed, and look like magic items.