Generally army rations consisted of little else than wheat. The soldiers themselves would ground the grain they were given and made it into things such as porridge or bread.
Whenever possible this monotonous army diet was supplemented with whatever was locally available like pork, fish, chicken, cheese, fruit and vegetables. But the basic ration of frumentum was never far from the soldier’s stomach and formed the basis of their diet. So much so, that when supply difficulties occurred in the grain supply causing other foodstuffs (even meat) to be handed out, there would be discontent among the ranks.
The officers enjoyed a more versatile diet (naturally). Archaeologists working along Hadrian's Wall in northern Britain discovered records of a commander from around AD 100; the records listed pork, chicken, venison, anchovies, oysters, eggs, radishes, apples, lentils, beans, lard and butter. Anyone else getting hungry? Not bad eating for a field officer!