Food and drink are very expensive in Rome, but you can find some very nice and cheaper cafes and restaurants if you get out of the main tourist areas.
There are hundreds of shops that sell souvenirs, but they mostly sell the same kind of things, rosaries and religious objects.
You’ll never be able to see everything in Rome in just a few days, but the easiest way to get a feel for the city is on an open-top tour bus. They charge about 15 euros and the ticket lasts 24 hours. You’ll be given a set of headphones that you plug into the socket next to your seat, and then you can listen to a continuous commentary of the sights you’re passing by. Just get off when you get to a place you want to visit and get back on another bus whenever you want.
San Pedro is amazing. Try to avoid the weekend as it is very busy, but during the week there is almost no queue. You have to go through the same security you go through at the airport to get in. If you go up to the dome, remember that there are hundreds of steep steps to climb. They have an elevator, but this only takes you to the base of the dome. Do not forget to visit the shop run by the nuns inside. Where you can buy rosaries that have been blessed by the pope. And keep an eye out for the Swiss Guards as you exit the Vatican. They look very colorful and smart in their orange, white and blue uniform.
The Colosseum will take your breath away. It costs 12 euros to enter but the queue is horrendous. For 20 euros join a guided tour. There are many people offering them outside. But be sure to pick someone who wears a license badge. You won’t have to queue to get in, and that in itself is well worth the extra 8 euros. You will get a full guided tour of the Colosseum, the Palatine and the Forum, which takes about 2 hours. And if you are lucky they will give you a ticket for a free tour in another part of the city.
Other sights not to be missed include: The Trevi Fountain (but watch out for the man with a magnetic stick who will steal your coin after you’ve thrown it), The Spanish Steps, The Pantheon, The Vatican Museum and the Sistine Chapel. .
Take some time to walk through the many winding back streets where you’ll find few out-of-the-way churches that look old and dilapidated from the outside, but will blow your mind when you enter.
Happy journey!