You may begin play with one item of exceptional value. It may even be magical, but the character may not yet know of its properties.
In order to begin play with an heirloom item, you must create a brief story explaining how your character came into possession of such an item. The story should not only reveal something about the item, but also about the person who carries it.
Most such items were handed down by the character’s family. Describe the relationship of the item to the family, as well as the family members themselves, and how they feel about the item, and handing it down. Of course, this item does not need to be magical. You will now have a tangible background, with roots and emotions that go deeper than most starting characters.
Alternate explanations are as varied as your creativity. The item might be on loan from an organization or patron. You may have found the item yourself, in a moment predating the character’s adventuring career. The item might be stolen, with an enemy to appear later, looking to get it back.
These items will be used at some point for a mini-narrative, spring-boarding into a broader story or adventures.
Once you have determined the story, sit down with the DM and work out the particulars of the item, such as powers and functions. Each character has a budget of 1500gp to spend on their item. You may have only one item each, and you don’t get to keep any leftover cash.