ATTIRE: Try to wear comfortable walking shoes as there is lots of walking throughout Europe. Layering is always a great idea as it temperatures may change from day to evening. Comfortable attire is best during the day for sightseeing and smart casual is best for evenings. It is not common to see the Europeans wear sneakers, flip-flops or shorts to dinner, though you may see tourists doing this.
IMPORTANT: to visit many churches, especially in Italy, your shoulders and knees must be covered, so make sure you pack a shawl for warmer months or bring pants/capri pants, or long bermudas that cover your knees. Skirts are ok for the ladies as long as they are below the knees.