Yes and no. Yes, a car can run on a mixture of alcohol and gasoline, also known as ethanol. A car today needs about an 85% mixture of gasoline to alcohol to run. In terms of the movie, this means the truck is running because there is already some gas in the tank. However, a car needs a special carburetor to run with only alcohol instead of gasoline, and regular drinking alcohol is not flammable enough to run an engine, even with the special carburetor. Fuel-grade alcohol is usually 100% alcohol, while beer and wine are around 8%, regular "hard" alcohol is 40%, and very few alcohols have 75%. Therefore, the truck in Gamer should not be able to run, especially with the "extras" added to the mix. That being said and given that the film takes place in the future, maybe cars at that time are equipped to run on alcohol instead of gasoline. However, it's very unlikely that store-bought alcohol can run a car, and the chances are even lower on a mixture of alcohol, vomit, and urine. In summary, the truck very likely could run because of existing fuel already in the tank, and what Kable did was probably completely unnecessary.