One thing I always check when flying European airlines is their baggage rules -- especially for carry-on. It seems like the probability of checked luggage problems increases with multiple stops and plane changes.
So this is a link to ITA's baggage rules: https://www.ita-airways.com/en_us/fly-ita/baggage.html
"The hand baggage you bring on board with you may weigh no more than 8 kg and measure no more than 55 cm in height, 35 cm in width and 25 cm in depth including handles, side pockets and wheels."
8 kg = 17.6 lbs.
55 cm x 35 cm x 25 cm = 21.6 in x 13.7 in x 9.8 in.
European airlines are very strict and it could be a real hassle if your carry-on is too big or too heavy. Hence this warning from ITA:
"Before proceeding to the boarding gate, check the size and weight of your hand baggage with ITA Airways ground personnel or by placing it in one of the baggage measurers near the check-in desk. The hand baggage of passengers who fail to perform this check may not be accepted on board."
ITA SpA also lets you bring an accessory of your choice from the following:
•Handbag
•Work backpack
•Laptop computer
No sizes are specified except there is this note: "The groundcrew will provide an “Under the seat” label for all small luggage (no larger than 36 cm in height, 45 cm in width and 20 cm in depth) for all domestic and international ITA SpA flights for all destinations."
I'm guessing, accent on the guess part, that relates to the potential maximum size of the accessory, 14.2 in x 17.7 in x 7.8 in. Someone please correct me if that's wrong.
Be sure to go to the Checked Baggage section for details on luggage checking requirements and especially for what you're allowed "depending on the travel class and destination" which is detailed in a table.
I've never changed airlines due to their baggage rules, but I've definitely changed what I packed for the trip.