Fuel questions
 

How much gas is left when the low fuel light comes on? What are your estimates of fuel consumption in an hour of sitting idle such as a situation where the car is being warmed up in winter. Thanks

1 min or 2 of warming up at idle doesn't use that much fuel... unless you're "warming up" for like 10 min... which is somewhat useless since you would still need to drive like a turtle to warm up the transmission...

low fuel light usually gives you around 50 miles... but you should still fill up asap since it's better for the fuel pump.

I was asking more out of curiosity, the minuscule amount of gas used isn't an issue but it would be cool if somebody could figure a test to see how much has is used in an hour of idle or how long it takes to idle away 1/16 of a tank.

You could just plug in an OBDII reader and see how much fuel the injectors are squirting into the engine at idle.

If I fill shortly after the light comes on, it takes ~11 gallons till it's full. Tank is, what, 13 gallons? Leaves ~2 gallons until completely empty, assuming it will actually run itself dry.

what parameter would show this information?

Yep, 13.2 gallons:
http://www.scion.com/cars/FR-S2014/specs/

I typically count on having about 30 miles of driving range once the low fuel light comes on, though that's pretty conservative given that I get 33 mpg combined city/highway. But as already stated, most fuel pumps live in the gas tank and use the fuel as a coolant, so running the tank nearly dry probably isn't the best for fuel pump longevity.

With frequent 10 minute warm ups (warming the car to melt ice not warming the engine to drive) my mileage went from a steady average of 7.3 L/100kms to a horrible 7.4 L/100kms! So not much is used.

I run Torque with a (usable) fuel reading in gallons. The low fuel light usually comes on when I have around 2 gallons remaining. That should give you 50 to 60 highway miles before the car quits.

Keep in mind that although it's a 13 gallon tank, you only have 12.5 gallons of usable fuel in it. That last half gallon can't be drawn into the fuel pump. A lot of manufacturers do this to give the tank an area where water and contaminants can settle without being sucked up into the fuel pump. The gauge on Torque actually shows 12.5 gallons when the tank is full.

Ten out of fifty litres remain, giving me about 125km with the light on. As Robr and FlamingRacecarSyndrome suggested, I try to preserve my fuel pump.

I fill my tank until the first click/stop, and reset the trip odometer. The next time i fill the tank until the first click, I've used about 40 litres and driven about 500km. That's 8 litres per 100 km. That's 10L/125km

Manual says i have a 50 litres per tank.

I spent about 10 algebra points and 5 mana points to cast that calculation. I have none left to perform it in imperial.

I've idled for about an hour and it cost 1L/100km on a tank. Not enough to be consistent or make conclusions.

Mine as well.

I only warm up until the revs drop signifying that the cold start cycle has finished. Usually takes 30 seconds to a minute.

After that I drive lightly, shifting at 3000 RPM for the first five minutes until the temp reaches normal levels.

Empty light consistently comes on exactly when my Scanguage II precise fuel level percentage hits 18%, full level on fill up is 95% consistently. Usually takes around 10 gallons to fill up.