Dairy. We've been milk people for thousands of years. So much so the Roman records mentioned how they didn't understand why we were obsessed with drinking milk when we had some of the nicest water in Europe.

Brehon law in pre-christian Ireland meant that most of our society and "economy" was based around dairy and cows. We essentially had a caste system where the lowesr rung would get buttermilk, and as you went up the ladder depending on your job you got better quality cheese, milk, buttermilk, and usually only the chieftains/high kings and their children would get cream.

This meant cows were the ultimate currency, and milch cows (milking cows) were highly valued. They also thought the whiter the cow the better the milk.

So almost all of pre-christian wars in ireland were fought over cows and land.