A stash of money that's been set aside for a large project is a war chest. In politics, money donated before a campaign starts is often called a war chest.
A war chest is generally set aside in case of surprising opportunities or unexpected circumstances. In business, a war chest might be used to expand quickly by buying real estate or equipment, for example. If your T-shirt business falls off after a busy summer, you'll be glad you have a war chest to tide you over until the holiday season. In sports, this term could refer to the budget for new players. Medieval war chests were literal chests full of money used in times of war.