Defense, roads, security, law and order, communications networks, large national things that serve everyone.
The government should be thought of as the business that does those things in a political science sense. Since it's so big it direct bills us all for its services.
Really the only thing that makes it a special case is that because it has all the guns and power of physical force, it has to be held to special rules through contractual obligation with the people, and it can exert unlimited power unless that contract is held to.