The most important aspect of this question is who is travelling, because that changes things a lot. For example, do we have a large army, are we talking about a pilgrimage or a royal family travelling across the country. Here are some of the things I managed to find.

According to Alexander Neckam, a wandering clerk of the 12th century, would buy his food in the town he was bedding down in. The inn chef would cook it (a chicken, some bread, etc). He would have some for dinner and the next day would set off down the road again, the leftovers in his pocket(check out Daily Living in the 12th Century by Urban Tigner Holmes, Jr.). Lunch was taken by the side of the road.

We also have pictures of peasants taking simple meals in the fields,  a bowl of something (soup? beer?), bread, cheese. 

It’s interesting to note that medieval folks had their own convenience foods.  There’s a recipe in Granado for “hordiate” (barley gruel, often served to invalids) that one can take on the road. You can find a recipe here.

 You can also find something in this book. Food on the move

Henry Marks in ‘Byzantine Cuisine’ mentions the Krivani (“domed metal or pottery top […] cooks bread faster and more evenly).

Voukellon is a thin, double baked bread used by the armies of Byzantium; the bread is soaked in liquid prior to consumption to soften it (and probably to add some flavor, depending on the liquid used).

Organized armies did travel with large groups of camp-followers; presumably they would have included butchers/bakers and people to cook for a bunch of hungry soldiers.

Here you can read some more ideas, as well as recipes for some of the meals.