What cocktails can I make with just a bottle of bourbon?

Old Fashioned (with sugar, bitters, orange peel), Mint Julep (with mint, sugar, crushed ice), Whiskey Sour (with lemon and sugar), and bourbon-and-soda or bourbon-and-Coke as long drinks. With one bottle and basic kitchen stock you can make four legitimate classics.

Bourbon is one of the most cocktail-versatile spirits because it pairs cleanly with sugar, citrus, mint, bitters, and (if you have them) sweet vermouth and Cointreau. With just a bottle of bourbon and kitchen pantry items: (1) Old Fashioned — sugar cube, 2 dashes Angostura (any bitters work; Angostura is the canonical), orange peel. (2) Mint Julep — 2 oz bourbon, 1 tsp sugar muddled with 8 mint leaves, fill with crushed ice, swizzle until the cup frosts. (3) Whiskey Sour — 2 oz bourbon, 0.75 oz fresh lemon, 0.5 oz simple syrup, shake hard, served up or over rocks. (4) Bourbon Smash — bourbon, lemon, sugar, mint, muddled and shaken; closer to a Whiskey Sour with mint. Add a single bottle of sweet vermouth and the range explodes: Manhattan, Boulevardier (with Campari if you have it), New York Sour (Whiskey Sour with a red-wine float). Add Cointreau or a triple sec and you can build a Bourbon Sidecar. One bottle of bourbon plus one of vermouth plus one of bitters is the foundation of a serious home bar; everything beyond that is variety.