So I was hungry at work and looked into the refrigerator at work and ate someone else's food.
What made you think it was okay to steal someone else's food?
Without their knowledge I ate some of their food
You are not entitled to someone else's food just because you can take it. Bring your own food and make amends with the people you've stolen from.
I guess that would be a better idea.
Or go out to eat that day. Spending money you didn't want to spend will help remind you not to forget to make a lunch for work.