Check your bag or pocket for your cell phone, see if it is undamaged and if you somehow have service. First, call 911 and tell them what happened (Though they probably already know) and tell them you think you're the only one who survived. Then, after ending the call, text your girlfriend or call her telling her you're okay. Check on your laptop and camera, and using the camera, take pictures of the wreckage, bodies and yourself in the case the authorities check to see if you're a terrorist or anything. Search for the flashlight you have in your bag and take it out and inspect the bodies one last time. Then enter the cars again and search for emergency things (crowbars, fire extinguishers, etc.) and crawl through the hole and run to the nearest platform.
(Retconning identity loss)
Hesitating, you stand back up and open your bag and pull out your cell phone. The screen is cracked, but you have a very faint signal, and the battery is about to die. Quickly, you begin to text your girlfriend.
"Michelle. I'm in a subway tunnel, I was in the derailment. I'm alive. Call the police quickly."
Just as you are about to hit the send button, the phone dies and you groan outwardly. You throw the phone on the ground, and pull out your camera. The lens is extremely cracked, and the flash is crushed, so you throw your camera into a fire. Finally you go to pull out your laptop.
Wait, where's your laptop?
You put your head in your hands, as the laptop had all your sensitive information like your tax returns. You put the bag strap back over your shoulder, and look back toward the train. There seems no other way back in after the ceiling collapsed, so your crawl through the hole in the tunnel wall.
On the other side, it's pitch black, but you see a faint blinking light in the distance. Desperate, you run toward it, but whimper when you find it's a flickering signal light. But, where there's signal lights, there's a subway platform. You begin to walk down the tunnel, when you finally find a subway platform.
Abandoned and fenced off.
It's more than likely that the entrance has been closed off, but you find a barrel fire and cot sitting on the far side of the platform. Tired, you lay down, close your eyes, and fall asleep.
