Tipping food carts workers
Most food carts in Tijuana are owner operated, but a few popular ones, like the HK tacos stand, employ many workers.
I can usually eat only 1 20-peso taco al pastor or 1 cup of birria soup, but I would put all my left over coins into the apron of worker serving me, most times about 2 x or 3 x the taco's price. That usually results in a taco with 2 x or 3 x the normal amount of the seared meat, delicious, not that I can eat that much.
The tacos stand would give a few soup refills free. But occasionally propinas would bring you extra birria in the soup.