Aperitivo usually contains a small amount of alcohol, enough to stimulate the appetite but not enough to get you drunk. The most popular aperitivo drinks are a spritz (white wine and sparkling water) or a negroni (gin, Campari, and sweet vermouth).
My personal favorite is the classic Aperol spritz, which consists of prosecco, digestive bitters, and soda water. It has a fantastic orange zest that makes the flavors pop.
While most Italians I've met prefer negroni or spritz, a select few also enjoy Campari, Cynar, and Lillet Blanc (the latter is French).