When shopping for liquor always buy the best brand that you can reasonably afford. Quality ingredients can make a huge difference, especially for cocktails served straight up or on the rocks.
People don't expect you to provide the same broad selection of alcohol as your favorite upscale bar.
The following is a list of items you will need for a basic home bar. Increase the amount of any items that you think will be the most popular at your particular event. For example, vodka is a popular alcohol served either alone or with almost any mix.
Shopping List
Liquor, Beer and Wine
2 bottles vodka
1 bottle dry gin
1 bottle scotch
1 bottle American whiskey
1 bottle rum
1 bottle tequila
1 small bottle dry vermouth
1 small bottle sweet vermouth
2 bottles white wine
2 bottles re wine
1 or 2 cases of beer (preferably a mix of regular beer and light beer)
3 or 4 bottles of your favorite liqueurs (coffee liqueur, amaretto and creme de cacao are ingredients in many popular drinks)