must sees not covered in RS Venice-Florence-Rome tour

It would be helpful to know what time of year you are doing the 17 day tour as suggestions may vary depending on the weather.

Clarification: you are taking the 10-day "Best of Venice, Florence, Rome" RS tour, is that right? And not the 17-day "Best of Italy"?

One fairly easy day trip from Venice is to Padua where you can see the Giotto frescoes in the Scrovegni Chapel (aka Arena Chapel). You could also go to Verona, or in the other direction to Trieste. Ravenna is wonderful if you're interested in the era of Emperor Justinian, but it would be a long day.

From Rome to see Pompeii in a day trip is doable and there are several tour operators that offer this. If you do it on your own, be aware you have to change trains in Naples and once you get to Pompeii it is some distance from the train station to the ruins (which are large and spread out -- an entire city). From Rome in the other direction, Tarquinia is famous for its Etruscan tombs. By the time you get to the Rome end of the trip, you'll probably have many other thoughts of places you'd like to see . . . or you may just want to relax and enjoy being in Rome!

Unfortunately Pisa is a day trip from Florence, not really reachable from Rome or Venice. But heck, you'll be seeing so many other fabulous sights. Maybe you can return to Italy another time and work Pisa into your itinerary.

Before the tour, you could spend time in Bologna. It's a rail hub, so there are plenty of places you can get to easily by train for day trips: Verona, Padua, Ferrara, Ravenna, even Florence.

Pisa is fine for a 1/2 day trip from Florence, but most of us would say it's too long a trip for too little to see, as a day trip from Rome or Bologna.

There are lots of things to see and do in Rome itself. Pompeii would be a really long day trip, but doable. Instead of Pompeii, go to Ostia Antica, the ancient port of Rome. It's very well preserved and from the same time period as Pompeii. Orvieto is a popular day trip from Rome.

sandy, when we did V-F-R tour, we flew into Milan, and stayed three nights in Varenna on Lake Como, then one night in Milan (to see Last Supper) before taking train to Venice. Very glad we did it that way. Also flying to Milan gave us direct flight options, and better fares. I think we could have spent the time enjoyably in Venice as well. Lots to see there that you don't get to on the tour.

There's no such thing as a "must see" that applies to everyone. Only you know what interests you most. Perhaps you're already doing this, but I strongly recommend getting the Rick Steves Italy book and review the whole thing, identifying what specifically interests the two of you most.

Happy travels.

If you decide on Padova, please note that you need to reserve tickets in advance to see the Scrovegni Chapel (can be done online). The visits are carefully regulated in order to preserve the frescos. Additional fine sights in town include St. Anthony's Basilica, the Orto Botanico, the Prato Della Valle, the Palazzo delle Ragione (markets), etc. It's ~1/2 hour from Venice by train, and trains are very frequent.

How many days are you going to have for your pre-Venice and post-Rome stays, and what time of year? Any mobility issues we need to be aware of? Any special interests besides Pompeii and Pisa (art, architecture, history, etc)?

There are a lot of suggestions we could make - and many you can do without tours - but some additional information would be helpful!

We are arriving in early June and we have 3 days before the trip starts. We will not spending extra time in Rome as my husband will be tired then. So let's just focus on your WOWs that the RS tour doesn't cover. I bought the book last year, but I haven't read it. I wanted the Best of Italy tour, but he doesn't like the moving every couple of days. And I was able to get tickets where we had some layovers so we don't have to continually fly 11 hours back to LAX and then wait for the plane to Palm Springs.

I'd deleted this suggestion as you'd already booked your flights but am putting it back in just in case you might considered changing them?

Personally I would have put your 3 extra days on the Rome end for a couple of reasons:
A. It's the largest of the three cities with the most ground to cover. The tour only allows 2 full days - not nearly enough - and if you want to do Pompeii, you need most of a full day to devote to the trip. The site is huge, and it takes some time to travel to/from Rome.

B. By the end of the trip you'd have a better grasp on how some things work in Italy and more confidence about striking out on your own. The extra days would also allow you to relax and catch your breath a bit before heading home.

We've not taken an RS tour, and it's been too long since I've been back to Venice but some suggestions for your free time in Rome...

Galleria Borghese: we enjoyed this one much more than the overcrowded Vatican. Reservations are mandatory, and sell out early for high season. This is a must-do if you enjoy art. Closed Mondays.
http://www.galleriaborghese.it/eng/galleriaBorghese.html

As previously suggested, you might head down to the scavi (excavation) of Ostia Antica. You could do this in an afternoon if you hustle (open until 7:15 PM in June). Directions by train from Roma Termini are included on the website. Closed Mondays.
http://www.ostiaantica.beniculturali.it/en/index.php

Churches: too many to mention but some of the best are San Giovanni in Laterano, Santa Maria Maggiore, Santa Maria in Trastevere, Santa Sabina, Santa Maria del Popolo and San Clemente, to name a few. The walk up the Aventine to Santa Sabina would be especially nice in June as it passes the municipal rose garden - with a nice panorama of the skyline and backside of the Palatine - and along the way you can peer through the keyhole in the gate of the Priory of Malta for a perfectly centered view of St. Peter's dome.

Florence:
Convento San Marco church and museum: the Fra Angelico paintings in the former monk's cells are wonderful as is museum's larger art collection. Walk over to nearby Piazza della Santissima Annunziata and visit the church of the same name (some excellent frescoes), admire the famous della Robbia tondi on the facade of Brunelleschi's Ospedale degli Innocenti, and look down the street from the piazza for an interesting perspective of his famous dome on the duomo.

Head up to Piazzale Michelangelo for a terrific birds-eye view of the city then climb the steps further up to San Miniato al Monte. If you time it right you could attend the monk's plainsong service:

"Sunday and public holidays the Eucharistic celebrations at 8:30 am, 10:00, 11:30 and 17:30. The celebration of 17.30 is entirely in Latin and Gregorian chant. Weekdays the monastic community celebrates the Eucharist at 7.15 and 17.30, both are in Latin and Gregorian chant."

https://www.visitflorence.com/florence-churches/san-miniato.html

A couple of other nice churches: Santa Croce and Santa Maria Novella.