Alcohol is a chemical compound used by people for a number of different things. During a zombie apocalypse, it is mostly used as a disinfectant or as an alcoholic beverage.
Any alcohol solution that is at least 80% actual alcohol is adequate to remove unwanted viruses and bacteria from an area. Isopropyl alcohol (more commonly known as rubbing alcohol) is commonly used for this purpose. Other disinfectants include hand sanitizer gels and wipes. If none of these are available, high proof liquors (generally around 150 proof) work well. However, since most liquors are only 40% alcohol, studies show that they are only 50% as effective, killing some germs but leaving others alive. In emergency cases (such as cleaning a wound) it is better than nothing, but far from sterile.
Alcohol can be used as a weapon by turning it into a molotov cocktail. It can also be used to start a fire. The amount of actual alcohol in the liquor is very important, as there are very few products that are 100% alcohol. When it comes to catching fire, the threshold is around 70%. Other ingredients of liquor can inhibit combustion. Because of this, many common liquors will not burn on impact or burn very little. Bacardi 151 is a good commonly available high-proof liquor that works very well. If used as a weapon, however, they are highly ineffective against zombies and can easily backfire on the wielder. High proof alcohol can also be used to suppliment gasoline for travel when low, although since the car was not designed for the differing levels of heat and pressure from a different fuel mixture, this is only recommened for short term/rare/emergency usage for fear of damaging vital car parts.
The only type of alcohol that the human body can process internally is methyl ethyl alcohol (also known as ethanol). Vodka is a liquor that closely compares to pure ethanol. There are countless variations of alcoholic drinks, as mankind has produced them since ancient times. The most popular groups are beer, wine, and liqour. The United States alone purchases around $90 billion worth of alcohol every year. Due to its lack of importance during and outbreak, there will probably be lots to go around.
Alcohol's mood-changing effects are well known. Depending on the dosage and whether or not it has been mixed with food, it can also cause dizziness, nausea, vomiting, decreased inhibition, poor reflexes, anxiety, loss of emotional control and loss of motor fuction. Long term effects of drinking can include all of those symptons (even months after stopping) as well as poor short term memory, and difficulty following the steps of simple procedures and simple problem solving (contrary to popular belief, Alcohol does not kill brain cells, but the effect might as well be the same). Long term usage has also been linked to faster onset of senility, depression (and depression related suicide), memory loss, decreased brain size, and higher risks of practically all types of cancer.
Alochol is an addictive substance (like a drug) whose withdrawal alone can cause death. Having a blood alcohol level of .04 (or 4/10ths of a percentage of your body mass) is fatal for most people, even experienced and weathered heavy drinkers. Overall, alcoholic beverages are a luxury and a social lubricant. They provide recreation at the expense of decreased logic and potentially lowered health. In a zombie apocalypse, letting one's guard down can be a fatal mistake. For this reason, survivors are advised to carry and use alcohol with caution.