My ability to carry on is influenced primarily by a few factors: number of shoes needed, the need to, “dress up,” and the weather. Actually, the first two are kind of related as dressing up usually necessitates an additional pair of shoes.
I have carried on to Italy for ten days, BUT it was with a youth choir trip, and we weren’t doing any fine dining. I did take a black skirt and a pair of dressy shoes, “just in case” on that trip (even with carrying on) but wound up not using either. That is a fairly small space way to have the capacity to dress up at least a little. Scarves and jewelry are also small and can make something dressier or not.
Weather can be more impactful - clothes and shoes for colder weather/temps tend to take up more space. I have never been the best at layering. I always wear whatever coat/jacket I am taking rather than packing it.