It is a common problem, but every car is different. After reviewing your car's design, I think there are three possibilities. I rure out the security system, because the your car will not even start without the right key. I also rule out the crank sensor, as I have not seen a bad one behave like that. Since it runs fine while driving, I rule out the fuel pump and regulator. When they fail, the car does not run fine sometimes on the highway--it may idle ok and go slow, but not the highway. So I am left with the two most likely reasons.
1. Intermittent fuel pump relay
2. Intermittent ignition switch.
To check the relay, swap it with the horn relay.
It the problem resolves, replace the horn relay with new.
If not, be prepared with a voltmeter or 12volt test light the next time it dies on you. Leave the key on, pull over, open the hood, and check for power on the 15 amp fuse #25 in the box labled ELEK IGN. If there is no power on yhat fuse, you have a bad ignition switch or loose ON wire from the switch to the fuse box.