I don't even have a driver's license so I might be way off, but...

Signal mirrors
A rag soaked in gas and a spark from the battery to make a fire. Anti-freeze or any such could probably be used as well.
A bulb, a car battery and jump cables = (heavy but) portable light source for signalling from a nearby hill.
If it was cold, I'd dismantle the back seat for extra insulation.
Webbing from the safety belts and any extra wire or cables.
Like Hikin Jim said, spare tires for black smoke and fire starters (I've never managed to ignite a piece of rubber from a spark, though). You could also cut them into rubber bands (shelter building, improvised hunting tools).

If really desperate, shatter one of the mirrors (at least my brothers 5-year old car still had real glass mirrors) to get a sharp edge. This would be enough to dismantle the seats at least.

A question to someone who knows better? Are there any metal containers inside a modern engine that could be used for boiling water? Easily removed and not coated/tainted with anything nasty, preferably.

I wouldn't drink the water from the radiator, but might boil it for hot water bottles and such.

-jh