The Happy Bag was a bribe paid by shopkeepers and inhabitants of Tortall to their local Dogs in the third century of the Human Era to ensure their help. The members of the Provost's Guard weren't paid much in that time, thus they needed the Happy Bag to support those with families and to pay for Dog's healers, medicines and funerals.
The Happy Bag was collected once a week. The practice was known from at least two big cities of Tortall: Corus and Port Caynn. It can therefore be assumed that it was collected in other parts of the country as well.
It is unknown if the practice continued into the fifth century of the Human Era.