1991 Chevy Cavalier STARTING

If your radio and lights turn off when the car quits then it is probably electrical. Have someone brave wiggle the wires by the battery when it's dark out and the car is running to see if somthing is loose.

It could also be moisture in the gas lines if it is getting cold out where you live. Not very likely if there is always over a 1/4 tank of gas in the car.

One other possibliity is one or more spark plugs are bad.

Try pressing down on the gas pedal to see if the car still quits.