There isn't a readily accessible, easily-operated "emergency fuel shutoff switch" like you might find on some larger vehicles or equipment on a 2004 Chevy Cavalier. The fuel system relies on various safety features built into the car's electrical and fuel delivery systems to prevent fuel flow in the event of a crash or major malfunction. These include things like the inertia switch (which may be under the dashboard or in the engine compartment, but its purpose isn't typically to be used as an "emergency" switch) and other electronic safety mechanisms.
Trying to manually shut off fuel flow in an emergency situation in a Cavalier would be very difficult and potentially dangerous, requiring specialized knowledge and access to components that aren't designed for quick user intervention.
If you have a fuel leak or other serious fuel system issue, call emergency services. Do not attempt to manually disable the fuel system yourself.
