Your foodstuffs would be seasonal, and some of them would be costly, but you would have a variety of options. Let's say that you are an ordinary Marcus Lycus living in Rome in the year 100 A.D--not poor, but not part of the elite either.

Your diet would to a great extent be based around three items: bread, wine, and olive oil. Bread was eaten with practically every meal--one of the earliest recipes for bread is by Cato the Elder, from 160 B.C. Wine would be your usual drink, and there would be many varieties, ranging from poor quality wines to the Falernian vintage, which was highly praised by ancient writers. (Sadly, we are not sure how to make it).

The lists of provisions scratched on walls in Pompeii provide evidence of other foods; they show purchases of food over an eight-day period. What did ordinary Romans buy and eat? The lists show bread, olive oil, leeks, onions, and cheese as regular staples, and on a couple of days fish and sausages. You could choose between different kinds of cheese, including some from quite far away. The Roman writer Pliny the Elder mentions that of cheeses from overseas, he prefers the ones from Bithynia in what is now northwestern Turkey, which indicates that cheeses from around the Mediterranean were available. Of course, if you're an average Roman, many of them are probably costly for you, and so you only eat them on special occasions.

In Herculaneum (a smaller town near Pompeii that was also destroyed by Mt. Vesuvius) archaeologists found a wide variety of food scraps. Based on this evidence, you could eat a wide variety of vegetables depending on the season--celery, cabbage, beans, olives, lentils. Since you live in Rome, you may be able to eat seafood on certain occasions; available options might include scallops, mussels, cuttlefish, sea urchins, sardines, eels, anchovies, and turbot. Spices and sauces to liven your cuisine would be dill, coriander, mint, and black peppercorns, the last of which would be imported all the way from India. Garum, a fermented fish sauce, would be used as a condiment for many foods. Fruits and nuts again were seasonal (unless the fruit was dried) and you could choose between figs, dates, apples, plums, pears, grapes, peaches, melons, cherries, and apricots.

Meat would be relatively rare and expensive for you, but chicken, goat, lamb, and pork would be available. Pork would be the most easily available in the city, so that would probably be your most common meat. Beef would be quite rare; it wasn't widely eaten by Romans, at least not in Italy.

Desserts would not be an everyday occurrence for an ordinary person such as yourself. However you could have them on occasion, and possible options include dates stuffed with nuts and pepper and cooked in honey, candied figs, or honey cakes.

This blog called Pass the Garum has some excellent ancient Roman recipes, with cooking instructions and recommendations: http://pass-the-garum.blogspot.com

Sources: Life and Death in Pompeii and Herculaneum

Pliny the Elder's Natural History