Advance train tickets and Ferry tickets

The seat reservation always come with the train ticket and tickets can be purchased up to 15 minutes before the departure.
Discounted fares are capacity controlled and can't be purchased on the same day of travel. Search trains departing in a couple of days for the routes you are interested in and see how many discounted tickets are still available. On the day you'll pay the full price, called "Base" (trenitalia.com) and Flexi (italotreno.it).

The only open tickets are those for the Regionale trains run by Trenitalia: at the station you pick a day of travel and a route, not a train and a departure hour. Regionale trains have no reserved seats and can't sell out, but the tickets must be time-stamped before getting on the train. Since they can't sell out and offer no discounts for early birds, most just get tickets at the station.

Imho the journeys you listed would be too long using the slow Regionale trains, but it's up to you.

The 5 routes you mention are best done on high-speed trains, although Bari to Naples is only served by local trains on the final short leg from Caserta to Naples. For example, Venice to Bari takes 8 hours even on the fastest trains. If you wait until 2 days before you travel to buy tickets, all of the discounted tickets may be sold out. Italo might have discounted tickets available after Trenitalia is sold out, but their trains tend to run less frequently and they don't service Bari.

Thank you both for your advice. The question I also have is, does it indicate on the Trenitalia site... which trains are high speed and which are locals? Naturally I would like to get the lowest price, but the routes that I indicated (in case of nesisity) do the locals trains still go to those places? even though they will be slower. Another way of asking is, can I still buy tickets on high speed trains, 1-2 days in advance, even though they will be be a higher price,? or could they be sold out, where as I can't take that train.?

The question I also have is, does it indicate on the Trenitalia
site... which trains are high speed and which are locals?

Any train labeled Freccia____ (Frecciarossa, Frecciargento, Frecciabianca) is a high-speed train. Regionale trains are slower and generally make more stops. There are also some local commuter trains - as in the case of the Circumvesuviana in the Naples area - that are not operated by Trenitalia, although you won't be needing that one.

For high-speed journeys between the cities, Italo is also an option and offers competitive rates. All of their trains are high-speed, and require seat reservations.

https://www.italotreno.it/en

Another way of asking is, can I still buy tickets on high speed
trains, 1-2 days in advance, even though they will be be a higher
price? or could they be sold out

Yes you can buy tickets at any time. It has been known for a train here and there to sell out but it's unlikely.

Thank you Dario Frank and Kathy, I will take your advice and look at the two websites.
Thank you, Peter

You're welcome. Still wish we could talk you into flying Venice to Bari as that is one loooong land trip. Your previous thread:

https://community.ricksteves.com/travel-forum/italy/train-travel-for-2-routes

Yes I know, but I have the time, and I think it will be partly Scenic along the coast. Can relax just getting off the flight from Atlanta. Just like in Switzerland we took the glacier Express, very long & scenic. I'm sure more than going to Bari! but that's just us. PS, in general, what cost more for these type of travel legs, high speed trains or the Flix & Marino buses?

Trains cost more than buses, but buses don't go 180 mph!

Using Regional (R or RV) or Intercity (IC) trains will add 2-4 hours to each of your 5 trips. If you buy tickets 1-2 days in advance and don't mind the longer travel times, you could use the Regional or Intercity trains to save money. However, if you're willing to purchase discounted Super Economy tickets on Freccia trains a few months in advance, you can travel much faster and more comfortably for about the same cost as the slower trains. The one downside is that Super Economy tickets lock you in to a specific travel time, as they prohibit changes after purchase.

Okay I understand most of that from the FA to the REG trains. So, you don't think I could get reservations one and a half days ahead of my trip on a FA or high-speed train? Your last drawback is what my concern was on some of the legs. I assume you mean on the super saver tickets. they are the exact time I'm booking, not just days? & can they be replaced and canceled for another time... Weeks or Months before we even go?

You can buy tickets for almost any train 1-2 days in advance, but you'll likely pay full fare that close to your travel date. Tickets for all high-speed and Intercity trains are for a specific train. Only regional train tickets can be used anytime during the day, and that's why they must be validated. There are 2 levels of discount fares for high-speed and Intercity trains (no discounts available on regional trains). The least expensive fares allow no changes, while the other level allows some changes with a penalty. You can find details of the restrictions on the Trenitalia and Italo websites.

Thanks again and I will check it out.

Peter, Trenitalia ticketing fare tiers and associated restrictions are explained here; click on "Base", Economy" and "Super Economy":

https://www.trenitalia.com/tcom-en/Offers

Italo ticketing fare tiers/restrictions are here (scroll down the page):

https://www.italotreno.it/en/the-train/fares

Super saver tickets. they are the exact time I'm booking, not just
days? & can they be replaced and canceled for another time... Weeks or
Months before we even go?

As Frank said, the very least-expensive tickets (Super Economy 2nd Class for Trenitalia or Low Cost Smart on Italo) cannot be changed or canceled without penalty. Tickets for all 'fast' trains will be for a specific train on a specific day at a specific time.

I'll note that we've only traveled 2nd class or similar on Italian 'fast' trains and been perfectly comfortable. There's no need, really, to purchase a business or 1st-class ticket unless you can land a really nice price break.

Thanks again I am looking at the two sites. Also Kathy, I've decided I will be flying from Venice to Bari.

Thanks again I am looking at the two sites. Also Kathy, I've decided I will be flying from Venice to Bari.