We have accounts for the boys. There are limits on what this money can be spent on. If a boy leaves the troop we will send the money to his new troop. If he doesn't join a new troop, our troop uses the money to support scouts that need help. We maintain the records in case a boy later rejoins.
As for the Scoutmaster deciding how the money is spent, that is not his job. As Scoutmaster, I have a budget to cover troop meeting (both mine and the boys). Commitee is responsible for most of the money.