The pre-potato Irish staples were cereal grains, mostly barley and oats:
These would have provided most of the calories for most people. Barley would have been eaten as bread, beer, and soup/pottage/porridge, and oats as soup/pottage/porridge and dense flatbreads/cakes.
Wheat was also grown, but was much less common than barley and oats in the early Medieval period. Wheat grew in popularity over the Medieval period, but remained behind the Big Two of barley and oats. Much of the wheat would have been eaten as bread.
Rye was grown, but in smaller amounts than wheat.
Common vegetable crops included cabbages, onions, leeks, carrots, parsnips, peas, and beans.
Wild greens, such as dandelions, would also have been eaten.
The amount of meat eaten would have varied with class, with the upper classes generally eating more meat (especially pork). Cattle were commonly kept, for dairying and animal power. Dairy products were probably the main source of animal protein for the lower classes. Cattle were an important measure of wealth in early Medieval Ireland, reflecting their importance.
The situation in Ireland was similar to that of England, but with more oats and less wheat, more dairying, and less mutton (due to less raising of sheep for wool). For pre-potato England, see my answer in: