It's Bill that's spent the money on his cussed booze and gambling. Way of the Lawless Max Brand The gambling houses can do it, and so keep on breaking the law.
When Winnie tries to drink, Jesse stops her. Then Mae and Miles appear. Alarmed at Winnie's discovery of the spring, they kidnap her. Winnie learns that the music she heard comes from Mae's music box. She also learns the Tucks' secret: the water in the spring is magic and has made them ageless.
When the tuck shop is in a school, it is frequently the only place (other than the school canteen) where monetary transactions can be made. As such, particularly in the UK, they often sell items of stationery too, although food is still their primary source of income and customers.