To my mind, the point of the personal penitential practice is preparation for Easter, so splitting hairs over where the Lent/Triduum line is shouldn’t matter for our personal practice–Good Friday and Holy Saturday are the most intense days to prepare ourselves spiritually for Easter.
The Triduum is technically a separate liturgical season because the liturgy is different for these days than for weekdays of Lent–it’s a matter for the books and vestments. But for fasting and penitence, they should stay the same or even be kicked up a notch, in my opinion.
The real question to ask for “when can I eat chocolate/drink coffee/etc. again?” is technically not “when does Lent end?” but “when does Easter begin”? I would submit that the answer is the first liturgical act of Easter, the Easter vigil. I’ll be ending my Lenten penance after this service.