I would highly recommend that you check out Pass the Garum, a blog that focuses on recreating ancient Roman cuisine: http://www.passthegarum.co.uk/ (I'm not sure how much of the old blogspot content has been moved yet, but the old URL: http://www.pass-the-garum.blogspot.com/)

Just by the name you can tell that the Romans used garum, a sort of fish sauce (similar to what you might find in present day Thai cooking). Just looking at the front page of the blog, you can see that they ate porridges, cheese, hardtack/biscuits, and plenty more. Now, high class citizens would have a better diet, of course, but one of the empire's political goals was to keep the general populace fed -- see http://www.passthegarum.co.uk/#!Give-us-this-day-our-daily-grain/cu6k/54e9158c0cf2a1055e92ddbf. Apparently, eggs were quite expensive, a denarii per egg according to this post: http://www.pass-the-garum.blogspot.com/2014/01/poached-eggs-with-pine-nut-sauce.html (and oh my god does it sound delicious).