Plan your wardrobe in layers, no matter what the season. Rome generally has mild winters and hot, sticky summers. Heavy rain showers are common in spring and late fall, so bring some fashionable rain boots. Take a medium-weight coat for winter; a lightweight all-weather coat for spring and fall; and a lightweight jacket or sweater for summer evenings, which may be cool. Brief summer thunderstorms are common, so take a folding umbrella, and keep in mind that anything more than light cotton clothes is unbearable in the humid heat. Few public buildings in Rome, including museums, restaurants, and shops, are air-conditioned. Interiors can be cold and sometimes damp in the cooler months, so take woolens or flannels.
Dress codes are strict for visits to the Basilica di San Pietro, the Musei Vaticani, and some churches: for both men and women, shorts, scanty tops, bare midriffs, and sometimes even flip-flops are taboo. Shoulders must be covered. Women should carry a scarf or shawl to cover bare arms if the custodians insist. Those who do not comply with the dress code are refused admittance. Although there are no specific dress rules for the huge outdoor papal audiences, you'll be turned away if you're in shorts or a revealing outfit. The Vatican Information Office in Piazza di San Pietro will tell you the dress requirements for smaller audiences.
Many public and private bathrooms are often short on toilet paper so it's best to carry a small packet of tissues with you.