If you do want to stock a full bar, most needs can be met by having the following on hand:
Vodka Rum Gin Scotch Bourbon Blended Whiskey Tequila
Stocking a Complete Cocktail Bar
If you want to offer more cocktail choices, in addition to the standard bar consider also stocking:
Kahlua® or other coffee flavored liqueur
Creme de Menthe
Creme de Cacao
Brandy and/or Cognac
B&B® (Brandy & Benedictine)
Triple Sec or Cointreau
Apple Pucker Schnapps (for Appletinis)
Bailey's Irish Creme
Mixers and Garnishes
Depending on the cocktails you plan on offering, you may need any or all of the following:
Juices – orange juice, grapefruit juice, cranberry juice, tomato juice or V8, pineapple, lemon or lime juice (fresh squeezed when possible or Roses), Pomengranate
For fresh squeezed juices, you can estimate that the average lemon or lime will yield about an ounce of juice, an orange will yield between 1 1/2 - 3 oz. of juice depending on it's size.
Mixes – Bloody Mary mix, Margarita mix
Carbonated beverages – club soda, tonic water, cola, 7-Up or Sprite, ginger ale.
Flavoring ingredients – Angostura bitters for drinks like Old Fashioneds, salt, pepper or horseradish for drinks like Bloody Marys, confectioner's sugar for fizzes an flips, grenadine, simple syrup, cream of coconut, etc.
Dry vermouth if you plan on making martinis.
Sweet vermouth if you plan on making Manhattans.
Sweet & Sour
Salt or sugar for rimming cocktail glasses (for Margaritas).
Milk, half and half, cream, whipped cream or possibly even ice cream.
Coffee – for hot drinks and last call, no alcohol.
Garnishes like lemon or lime peel or wedges, orange slices, Maraschino cherries, olives, cocktail onions or celery stalks.