I've heard that one should not go empty-handed to a Guru. Is this mentioned in the texts, and how does it relate to the experience of devotees?

Yes, this principle is explicitly mentioned in the sacred texts. Chapter 35 states, 'It is not good to go empty-handed to the door of God, a priest, or a Guru.' This is illustrated by the devotee Kaka, who, on his way to see Sai Baba in Shirdi, bought two seers of grapes to offer. This act of offering, no matter how simple, sets the stage for receiving grace. In this particular story, the grapes Kaka offered became the very instrument through which Baba taught a profound lesson to the skeptical Boss Dharamsee. By transforming the grapes with seeds into seedless ones for Dharamsee, Baba used the humble offering to reveal his omniscience, dissolve doubt, and instill deep faith and love in a devotee's heart.