Complex sentence: The unique, noncommercial economy of Vatican City is supported financially by contributions (known as Peter's Pence) from Roman Catholics throughout the world, the sale of postage stamps and tourist mementos, fees for admission to museums, and the sale of publications.
Split into simpler sentences: The unique, noncommercial economy of Vatican City is supported financially by contributions (known as Peter's Pence) from Roman Catholics throughout the world. These contributions include the sale of postage stamps and tourist mementos, fees for admission to museums, and the sale of publications.