“groceries” is pretty vague without being intimately familiar with the neighborhood you’ll live in, your cooking/eating style, how you shop for groceries now, etc. Twice what you spend at home would be a starting point for budget. Altering your cooking/eating style to a more European version can cut that, but I think eating better, fresher food than at home is more likely than saving a whole lot from the 2 x home cost budget, particularly if you’re comparing to megamart food stores at home.

Some items you may be used to are almost never found in Europe. Frozen orange juice comes to mind. I’ve always found fresh fruit and vegetables reasonable; they have a lot of small places carrying them. Many places have prepared dishes that are reasonable. But we always have difficulty with canned and boxed goods that need preparation, because of our language deficiency. We once bought buttermilk by mistake, as it had a blue cap that we thought meant 1% milk. That was an unpleasant surprise on cereal.

I prefer bakery from a real bakery, but it often costs a little more than that in the supermarket. Bottled water is popular; we usually buy the largest bottle we can find to save a bit. Wine is very reasonable, even the most inexpensive is fairly good, so we have wine with our meals. We’ve often found very reasonable good food in neighborhood restaurants, so we have gotten in the habit of going out for lunch and dinner.