Usually, city governments will sponsor a large fireworks display. Cities like Seattle and NYC will launch them off a barge in th middle of a body of water. In my town, there’s always a baseball game with fireworks afterward, and there’s another show at one of the larger parks. The shows are usually accompanied by traditional marching band or orchestral music (usually recorded)—patriotic songs such as you’d hear at a military review or parade.
Also, lots of people take advantage of the long, summer weekend to go camping, travel somewhere, or shop theholiday sales (TVs, furniture, appliances, etc.)
In addition to the booze, food and fireworks gluttony mentioned, it’s also common for yahoos to fire their guns in the air—illegal, but common.