Food could get real expensive, real fast. I was eating fish while there, something I don't do at home, but no matter where I am won't eat flour due to the reaction I've experienced in the past from gluten. One day we went into a cafe for lunch and I thought I'd just have some fries, I ordered a large because the pile on a plate of fish and chips I saw included about 20 fries. I almost ate the whole bucket.
Most of our other lunches were peanut butter and jelly or cheese and crackers and a great Icelandic product, Skyr. We thought that was yogurt, it's similar to Greek yogurt, but it's actually cheese. Groceries weren't as expensive as restaurant meals, but then tipping isn't common there, and most places we visited were free so it worked out OK.