Supersonic flight

A supersonic aircraft flies faster than the speed of sound (661 knots at sea level). The standard fleet of FS2004 doesn't contain any supersonic aircraft (previously it did with the Concorde).

Aircrafts

There is plenty of free military aircraft add-ons at e.g. AVSIM. My favorite is this F-16 Fighting Falcon by Kirk Olsson together with this panel by Eric Marciano. This aircraft can reach a speed of Mach 2. If you make too fast manoeuvres at high speed you will face blackouts where the screen becomes black or red.

The Carrier Operation Package by Rob Barendregt and Doug Dawson (an add-on for aircraft carrier operations) contains a gauge where you will hear a sonic boom when you pass the sound barrier.

Jet fighter flights

Here is some suggestions for flights in a supersonic jet fighter:

Depart in your jet fighter from Nellis Air Force Base (KLSV) in Las Vegas, Nevada, and head east to the Grand Canyon. See how fast you can follow the Colorado River at the bottom of the canyon without hitting the hillsides, experiencing blackouts, or overstressing the aircraft. The terrain mode on your GPS navigator may be useful for this flight.

Escort an (AI) VIP aircraft from the departing airport to its destionation in your jet fighter. Alternatively if you have a radar screen in the aircraft panel (e.g. the F-16 by Kirk Olsson) you may takeoff from an airbase and locate a random aircraft on the radar to intercept. Actually intercepting aircrafts is quite difficult because you are required constant visual focus on the intercepted aircraft while controlling speed, altitude, and heading.

See this page on how to install aircraft carriers in FS. Depart from an airbase on the mainland, fly to an offshore located carrier and make it the base of your missions.