Few cocktails are as easy and refreshing as the gin and tonic. At its most basic, this highball is nothing more than aromatic gin and bubbly, quinine-flavored tonic water with a lime garnish. From there, it's easy to create variations on the drink. Try adding a little vermouth or a healthy dose of Angostura bitters. If you're feeling ambitious, try making homemade tonic water—you'll need citric acid, cinchona bark, and flavorings of your choosing.