Like the restaurant receipt, you'll want to keep the receipt they hand you in an Italian bar for at least 100 meters after you leave the place.
This is the receipt from a bar in Torino where I had breakfast, which consisted of a typical Italian morning treat: coffee and a croisant-like roll. The receipt has the address, telephone number, tax (VAT) number, and the things you've consumed.
In larger cities, you'll line up to get a receipt before you order your coffee. Then you'll belly up to the bar and show the receipt. Sometimes the barista will tear the receipt to keep tract of what's already been served. You're still required to take it with you when you leave.