ferry

Ask the rental car company what their policy/requirements are for doing that.

Most credit cards do not provide the CDW in Italy. You need to check with them as it varies

Couple things...

1. Not all credit cards are the same. You need to check - very carefully - where and when (in what countries and under what conditions) your credit card insurance is valid, and where/when it's not, and what it covers (and what it doesn't).

2. Make sure you get solid, reliable information - in writing - and be sure you understand it. The first person you talk to might be clueless or just plain wrong - so get it in writing (they'll send you an email to confirm what you discuss). As an example, I called my credit card company yesterday to confirm details of coverage for an upcoming trip to multiple eastern European countries, and the "insurance specialist" I spoke with was painfully ignorant (she was obviously just reading from a script; it quickly became clear to me that I knew more about the coverage than she did; the fact that she apparently had never heard of the countries I was going to, couldn't find them in her system and badly mangled the pronunciation of the country names as she read things to me did not instill confidence...so I'll be calling back again in a few days in hopes of speaking with someone there who actually knows what they're talking about - if you get squishy answers or a clueless person like I did, thank them, hang up, and call again later).

3. Know about what you must do (and must not do) when the moment comes at the car rental counter when they offer their own insurance. This may be critically important because if you make the wrong choice there, it may invalidate your insurance. Exactly what to do about this depends on the country you're renting in (some countries, including Italy IIRC, require you to buy at least some insurance with any rental). OTOH your credit card company's insurance probably has a clause that states if you accept any offer to purchase insurance from the rental agency, your insurance from the credit card company is not valid. So it's easy to find yourself with a dilemma and not know which way to go. You need to know exactly what to do about this before that moment comes (and the answer is not always the same in all cases).

4. You must read (and understand) the fine print in the car rental contract, too (not just the credit card/insurance details). On my rental contract, the terms and conditions included a clause whose language essentially said "Car can not be taken on a ferry". You can get them to remove that clause (and explicitly say ferry travel is allowed) but if you don't...you leave yourself very vulnerable. This is not something you can do at the rental counter; nail down all these details from home, long before you leave for your trip. It's stressful enough to land in a foreign country then (when you're jet lagged, struggling with language issues, disoriented, and feeling pressure from the line behind you) that's not the time to try and sort out these complex details. Get it all down before you go.

Me, I'm almost done preparing to drive my rented car around Latvia. Hope the above helps. Have fun in Italy. :)

First thing you need to do is confirm that the rental company will allow you to take the car on a ferry. Some don't.