A Roman drinking glass
Most people in the Roman Empire lived mainly on the usual foods of people living around the Mediterranean Sea - barley, olive oil, and wine, which we call the Mediterranean Triad. In addition to being full of carbohydrates, these foods provided fat (the olive oil) and protein (the barley). If you were rich, you could also eat beef, pork, lamb, chicken, and fish, dormice, and snails. If you were poor, you ate mostly just the Mediterranean Triad, with vegetables like lentils and cucumbers and lettuce, fruit like apples and figs, nuts, and sometimes cheese and eggs.
People also ate different food depending on where they lived in the big Roman Empire. In Egypt and West Asia, most people didn't eat pork. In northern Europe, some people drank beer instead of wine, and got their fat from butter instead of olive oil.
Rich people's food (with recipes)
Poor people's food around the Mediterranean
in Northern Europe and England
in West Asia
A rich Roman's dining room (triclinium)
To find out more about ancient Roman food, check out these books from Amazon.com or from your library:
Spend the Day in Ancient Rome: Projects and Activities that Bring the Past to Life, Ages 8-12 by Linda Honan (1998). With recipes for a whole Roman feast, for kids.
Roman Cookery: Ancient Recipes for Modern Kitchens, by Mark Grant (1999). Recipes for the food ordinary Roman people ate, not the fancy stuff.
Ancient Roman Feasts and Recipes Adapted for Modern Cooking, by Jon Solomon (1977). A history of Roman food, and then about a hundred Roman recipes you can make.
Food and Society in Classical Antiquity, by Peter Garnsey (1999). Garnsey has written a lot about ancient food, and is an expert, but he writes very clearly.
The Classical Cookbook, by Andrew Dalby (1996). Both rich and poor people's recipes, with a lot of context too.
Around the Table of the Romans: Food and Feasting in Ancient Rome, by Patrick Faas (2002).
Here's a good webquest about Roman food, if you're interested.