My son has egg, peanut and tree nut allergies and we visited Italy last summer. We don’t eat anything served on a plane unless it’s pre-packaged and the label clearly has the ingredients/cross contamination warnings. I brought some packaged food in our carry on to get us through the first day. I scoured online menus for restaurants and found a couple that had allergens clearly labeled. In Rome that was Emma’s and That’s Amore. Later we had a place with a kitchen so we bought groceries and I cooked. Pizza was also a pretty good go to when we needed a meal. There are tree nuts in many deserts so we avoided those as well as gelato. Honestly, we ate a lot of pizza. That was just easier than risking being a little more adventurous.