Keeping a jerry can of gasoline in your car may help if you run out of fuel, but it's also highly dangerous and is therefore illegal in most places. According to the Makers of Magic Tank Emergency Fuel, their product is the safe – and legal – alternative to packing a jug of gas.
When Magic Tank is poured from its container into a car's fuel tank, it will apparently allow the vehicle to continue traveling as far as it could using an equivalent amount of gasoline.
The liquid is derived from gas, but contains "no volatile butanes, pentane, hexanes or heptanes." To you and me, this means that it's officially designated as non-flammable. It will ignite if exposed to a spark or flame at a minimum temperature of 105ºF (40.5ºC), but that's far higher than the flash point of gas. It's also biodegradable, and reportedly won't harm the engine.
So, if the stuff is so much safer than gas, why not just run your car on it all the time? Well, because it works by displacing the residual gas that's still in the bottom of the tank – even when your car can't go any farther – pushing that gas up so it can be used by the engine.
Magic Tank is available via the link below, with prices starting at US$29.99 for a half-gallon (2-liter) bottle. For those of you who might remember Spare Fuel or Extra Fuel, it's the same formulation as those now-defunct products.
Source: Magic Tank
This statement is entirely misleading. If you pour five gallons of this stuff into the tank and it displaces whatever gas remains in the tank, say 2 gallons, and it is not a fuel in and of itself then there is no way you could get equivilant distance out of equivilant amounts.
Otherwise I don't think it's a good idea to use the last drops at the bottom of the tank. Usually it's full of small debris, dirt, etc. I think, even your car's injector nozzles could be clogged....
All cars today have an idiot light to warn operators of a low fuel level. If that isn't enough to motivate, then actually running out will be a good lesson.
I knew I had 160 miles left when it said "empty" (I experimented) And I hate filling up. So I estimated and it worked, mostly. I ran out about 5-7 times over an 8 year period. I was so irritated I decided to sell.
I still wonder what the manufacturer's reason was for this design.