RAILS was a breakfast food first mentioned in Grand Theft Auto: Liberty City Stories.
The cereal references cocaine, in that the name is a slang word for the drug, the cereal is consumed by snorting it up the nose, it resembles a white powder, and the side effects (nosebleeds, addiction and an inflated ego) resemble cocaine's. It was featured in the Liberty Tree article, RAILS Breakfast Cereal Under FDA Scrutiny, written by Beverly Clamhopper, which discussed how the controversy over the side effects had led to an FDA probe and a recall.
There is confusion over which company manufactures the cereal: the packaging mentions Biglogs, the GTA Liberty City Stories website mentions Colombian Breakfast Inc, and the Liberty Tree article mentions Mendez Foodstuffs of Medellin.
The cereal is apparently still sold in Grand Theft Auto IV, as it is advertised on the Biglogs website and on small posters around the city, it also appears at Trevor's safehouse at Sandy Shores in Grand Theft Auto V.
RAILS were first introduced in 1997, according to the Grand Theft Auto: Liberty City Stories manual. (They were brought on to the market "last year", and LCS taken place in 1998.)