Overhead luggage rack on Italian rails

Yes, plenty of luggage racks overhead that handle carryon size bags. Take the Freccia trains and you will not have that many stops. From Termini, you will stop at Rome Tiburtina, Florence S M N, Bologna, and maybe Ferrara, So there will not be that many opportunities for hop-on/hop-off thieves.

There is also storage for your bags in the spaces between back-to-back seats.

And keep in mind that luggage theft is extremely rare. The locals dump their luggage in the storage bins all the time. And if my memory is correct, there has been only one report on this site of luggage disappearing. We do take the precaution of slipping a small cable lock between the handles of our luggage when put in the storage bins. Thought being that if one piece of luggage was grabbed, the second attached piece acts as an anchor and a surprise to the grabee. In 20+ years of train travel all over Europe in all kinds of trains we have never had a problem. We would not give it a second thought about throwing our luggage in the luggage bins.

You can fit also bags that are larger than what airlines allow as carry on. I've fit my wife's (heavy) midsize bag (my wife badly needs a class on packing light).

You can see the image here on the so called Standard Class on Frecciarossa trains (this is the lowest class).

If you upgrade to a higher class the seats are larger, because the configuration is 2+1 instead of 2+2, but the rack seem similar in size. This is a photo in Business Class

If you have large pieces and need to put it in the hold at either end of the car, travel with a cable lock and tie them together.

We were able to put 25" Samsonite rollers on the overhead shelves on both the Trenitalia and Italo trains.

Some trains also have luggage bins in the middle of the car.