From the back cover:
You can now determine how many gemstones are set into that bejeweled cup; or what the King will think of the magical saddle that you have found. Inside this book are full discussinos on the nature of wealth in a fantasy role playing game. Also, the long awaited Alchemist profession, is now added to the RMSS.
In Treasure Companion you get:
A discussion of the concepts and premises behind treasure, wealth and the effects they have in a GM's game world.
Guidelines on how to mesh the rules for alchemy presented in this book into the RMSS, buying and selling magical items, and ways to customize the treasure generation tables.
Three new Alchemist professions.
22 Alchemist spell lists.
Complete tables for generating all types of treasure (including a detailed system for generating gemstones and jewelery). All magic items generated from the tables can be created using the spells presented in this book.
Complete item descriptions for over a hundred unique magic items.