Hmm. Wikipedia disagrees. "Dry gas is an alcohol-based additive used in automobiles to prevent any water in the fuel from freezing, or to restore combustive power to gasoline spoiled by water."
http://en.wikipedia.org/wiki/Dry_gas

But then again, that's from Wikipedia. Best taken with a grain of salt (or a dram of good ethanol).

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I haven't heard the term "dry gas" before now -- is it a brand name?

If the gas at the pump has 10% ethanol, there probably is no need to add more alcohol to prevent gas-line freezing.

In my part of the world, when temperatures drop well below -30C, freezing of water in the fuel system can leave you stranded. I have seen this many, many times. A couple of small bottles of methyl hydrate is standard in my winter kit, and it has saved me and others from a lot of grief. I last used it when the temperature dropped below -40C and I had to park the Mazda for three hours (social obligation). She would sort of catch, then nothing; I dumped a bottle of methyl hydrate in the tank, went back inside to the refreshments table, and half an hour later she took right off. The trick is to recognize the problem and stop cranking before your battery is dead.

For people who have heated garages, SOP is to keep the fuel tank full or mostly full. This reduces the amount of warm air (with its entrained moisture) that can enter the tank and, over time, accumulate.