I would guess anything that doesn't involve exchanging money for an object or experience, in which the quality and/or duration of the object/experience increases with increased cost.

Some ideas off the top of my head:

- Volunteering your time locally in your community (soup kitchen, tutoring underprivileged kids, coaching youth sports, etc.)

- Building interpersonal relationships with new people

- Putting work in to maintain existing interpersonal relationships

- Meditation, mindfulness

- Building a tangible skill that takes intense study/practice over a time scale of multiple years to be considered an expert (craftsmanship, visual arts, martial arts, athletics, etc.)