It really depends on the area/state. You're coming to Florida? There are usually fireworks displays in mid-sized to big cities, but if it's a particularly dry year and if there is a high forest fire risk then the fireworks displays may be cancelled.
I can only speak to what my hometown does (Port Orange, a suburb of Daytona Beach). There's a city center area with a large lake in front of the city hall. There are tons of booths around the lake selling burgers and hot dogs and BBQ, stages set up for live music and performances, laser shows, bouncy houses for kids, etc. People set up their blankets on the grass and wait for the big show. After that we usually went back to our house and set off a bunch of fireworks in our driveway.
I'm not sure about stores closing early, but I don't think they do.