Rome to Pompeii and back in 1 day

We used Mondo in 2023 and were happy with it. Pompeii is huge and depending on your level of interest you could easily spend several hours there-we spent 12 hours over 2 days. The Mondo tour will be 2 hours and will only cover some hilites. I see Mondo also has an 11:15 tour. I'd recommend that time slot to give yourselves extra time afterward.

There are plenty of of restaurants outside of the main gate to eat. As for how strict they are bringing snacks, there are signs that say you can't, but when we were there everybody was sitting on curbs pulling food and drinks out of their bags. We didn't bring anything in so I have no idea if they check bags or not.

There are many posts on this subject that you can peruse. Many do not recommend daytrips to Pompeii from Rome. You could look at doing Ostia Antica which is about a half hour on public transportation from Rome. It is described in the Rick Steves guide. It is cooler, smaller, less busy and lovely.

We brought water bottles and snacks into Pompeii. To get to Pompeii Scavi, we took the high speed train to Naples. We purchased that ticket in advance. From Naples, there are a few options. We choose the Circumvesuviana train. Make sure to get off at Pompeii Scavi. We saw Pompeii on the way to Sorrento.

In 2022, my brother and I did that exact trip: Rome to Pompeii and back in one day. We left about 8 a.m. and were back by about 7 p.m. We had pre-purchased via the internet a fast-train ticket on Tren Italia and got to Pompeii in 1 hour, 15 minutes, I believe. (Note: Tren Italia has a competitor, whose name I cannot recall, but you can price a competing run, if you want.) The regular-speed train would have take about twice as long. From the Naples train station, I had pre-purchased a bus ticket that took us the 20 miles to the Pompeii site. (I cannot recall the name of the bus company at the moment, but if you need it, let me know.) That took us to the gates of the archeological site, and I had pre-purchased the entry tickets.

After we took the bus back from Pompeii to Naples, we had planned to have pizza at Antica Pizzeria Port'Alba, which claims to be the world's first pizzeria. There was a line out the door and around the block. And L'Antica Pizzeria da Michele -- which claims to be the world's second oldest pizzeria and is near the first one -- also had a line out the door. See if you can make a reservation at one of them. If not, there are millions of eateries in Naples around the train station, and they all looked good.

We went to both Pompeii and Ostia Antica in April this year. Both were really interesting but I liked Ostia Antica more. It is still huge (we were there 4 hours) and has a nice cafeteria inside the grounds so can have a lovely break in the middle of your exploring. If you do go there, be sure to buy the map (4 euro). It was well worth it.
It wasn’t the difference in ease of access that made me like Ostia Antica more. We stayed in Naples when we visited Pompeii (so easy train trip) and Rome when we visited Ostia Antica (easy commuter train which is included with bus/metro tickets so just 1.50 euro from anywhere in Rome). Ostia Antica was beautiful and less busy. Also, easier to get away from groups!

Month of year? Heat and sun are HUGE factors in visiting sun-bleached, Roman stone road, treeless Pompeii. Especially from May to September.

Your Pompeii ticket will not permit you to exit and re-enter the same day. So it might be wise to plan on the glorified cafeteria (air conditioned, with hot food) inside Pompeii (but not inside Herculaneum.) There are one or two hotels near the Porta Marina entrance (Circumvesuviana train stop ... ) so they might have restaurants, but it's not a bustling part of the modern city of Pompeii. This is not a day to expect gourmet dining, served as 2-hour "slow food."

We didn't visit Pompeii until our sixth or so trip to Italy, when we finally saw Sorrento and the Amalfi Coast.

https://community.ricksteves.com/travel-forum/italy/pompeii-day-trip-from-rome-2c38f926-9036-480d-95fd-403dd7694e4a

We made that day trip back in March. Yours sounds marginally easier than ours because you are staying near the station while we had to get from Piazza Navona to the station as well. It was a full day but I am glad we did it.

The worst part of the day trip is the local train from Naples. The train was packed even though the park was very quiet.

The restaurants at Pompeii Scavi were underwhelming. I would get pizza in Naples before taking the train back to Rome.

We brought water bottles into the park. Our guide was encouraging people to fill up in the fountains in the park.

We also went to Ostia Antica on this trip (we had some downtime the last day and were staying at the airport). I much preferred Pompeii. But that was with both parks being pretty empty and the weather was mild. If you will be traveling when Pompeii will be busier and hotter, then maybe I would change my recommendation.

I have been to both ( different trips) and given your "...but time is limited" I think doing Ostia would be a better choice.

Each has unique features but many similarities of what ancient Roman life was like.

Folks have done what you propose but usually comment "it was a lon-n-n-n-g day'. What are your plans for the day after?

Pompeii is best if you are there first thing with a pre-bought admission ticket when the entry gates open at 9am. This means your group will be ahead of the throngs entering the archaeological park ( Pompeii allows 20,000 daily visitors) by mid-morning, and it also means you’ll get a jump on the heat of the summer months.
There are two trains that depart Roma Termini at 6:00 arriving at 7:12am (Italo) and a second Trenitalia train departing at 7:00am arriving at 8:12am. It takes another 40 minutes to take the Circumvesuviana train from the Garibaldi station downstairs from the Napoli Centrale station to the Pompeii Scavi station.
Bring hats, sunscreen , water bottles and food with you. You can eat in designated picnic areas inside the archaeological park.
Enjoy!

What time of year?

Take the train from Roma Termini to Napoli Centrale, get on the Circumvesuviana direction Sorrento, get off at Pompeii Scavi. Enjoy your time at Pompeii. When you're done, exit through the gate by the amphitheater and walk into the center of Pompeii town for a meal. Then it will be a quick walk to either the Pompeii station on the Circumvesuviana (different from the one you got off at) or the Pompeii station on the commuter rail. Your GPS app should be able to give you the next departure time so you can decide which is best. Or you could return to Pompeii Scavi and get something to eat in Naples. Return to Napoli Centrale and get on your train back to Rome. I would bring a meal on the train if you're concerned about being hungry in the park but you don't want to chance bring food in. Totally doable in one day.