Peter, It is possible to do it all in a day, but it will be a long day. You would start by taking a train from Rome to Naples, and depending on the train this will take 1 1/2 - 2:10 min each way. Once you arrive at Naples, you would than catch the Circumvesuviana Line (this is a private train company) which goes to Herculaneum (about 20 min) and on to Pompeii (get off at the Pompeii Scavi stop) which is another 20 min. You could do this in either order and at the first ruins you can buy a combination ticket that will get you into both ruins. As to food, there are a groups of cafes/restaurants across the street from the Pompeii entrance. These are pretty touristy cafes, but you will not go hungry. Herculanuem is actually in the middle of a town and you can walk from the ruins to many cafes and restaurants that are all within a few blocks. I understand that they now are running high speed trains on the Rome-Naples line that make the trip in about 1 1/2 hours, and of course these trains would help maximize your day. As to the ruins, both areas are wonderful and different enough that it is very interesting to do both in a day. We were in Italy for a few weeks this past May and happened to spend a week in Praiano along the Amalfi Drive. On "Mothers Day" my wife said she wanted to go to both ruins (we had been to these sites on previous trips) so we did both places in a few hours. Despite having done this before, we still enjoyed every minute.