At level 9, the Rogue’s Phantom subclass (Tasha’s Cauldron of Everything) gets the ‘Tokens of the Departed’ feature, allowing them to create ‘soul trinkets’
When a life ends in your presence, you’re able to snatch a token from the departing soul, a sliver of its life essence that takes physical form: as a reaction when a creature you can see dies within 30 feet of you, you can open your free hand and cause a Tiny trinket to appear there, a soul trinket.
These trinkets have a couple of uses, one being:
While a soul trinket is on your person, you have advantage on death saving throws and Constitution saving throws, for your vitality is enhanced by the life essence within the object.
Given that you can have more than one soul trinket at a time (up to your proficiency bonus), it’s tempting to pass them around. It’s unclear whether the quoted soul trinket benefit is a property of the trinket or of the rogue, and hence unclear whether another character holding a trinket would gain advantage on death and Constitution saving throws.