What are the ingredients and preparation method for a classic boilermaker cocktail?

A classic boilermaker cocktail typically consists of a shot of whiskey served alongside a glass of beer. To prepare, simply pour the shot of whiskey into a shot glass and serve it alongside a glass of beer. The drinker can choose to either sip the whiskey and beer separately or drop the shot of whiskey into the beer and drink it as a "boilermaker" shot.