At least as early as the first century AD, tabernae served simple food and drink to patrons. According to Hospitality: A Social Lens (Lynch, Morrison, Lashly; 2007):

They usually contained a simple L-shaped marble counter about six to eight feet long, with a simmering pot of water and shelves of other food on the back wall of a tiny room, often just large enough for the proprietor and several assistants.

The Greeks also had thermopolium, example of which can be seen throughout Greco-Roman ruins. Here's a little YouTube video where you can see that L-shaped counter.

In terms of the menu, I've heard simple flatbreads were common items, but that's personal conjecture and I'd defer to anyone who specializes in the actual foodstuffs of the day.

I read somewhere (no idea where, sorry) that what we would recognize as restaurants didn't arise until the late 17th or early 18th century. Was this the case? If so, what would travelers have done (apart from bringing their own provisions) to ensure they had food?

hi! you may be interested in these

• Did Ancient Rome have any restaurants? Places where people would sit and order food and socialize? If not, then when did restaurants become the norm?

• What was it like to "eat out" during Roman times? Was there a wide variety of different restaurants and foods to choose from? How often could the average working person afford to eat out?