Although there is no official catering on the IC trains, as I have mentioned before, there is usually an enterprising Neapolitan gentleman patrolling the train selling filled rolls, soft drinks and mineral water from a shopping trolley. While the supermarket/deli/picnic option is infinitely preferable, the free enterprise option is OK for emergencies, if you don't mind eating cheap processed cheese and ham. All this is highly illegal of course, but no one takes any notice of the rules South of Naples and the train crew turn a blind eye. (They probably get a free sandwhich or two from the vendors!)
Even the sleeper train on the 1000-mile run from from Milan to Syracuse, via the ferry, had no catering a few years back when I was on it for about 18 hours or more (less a quick nip up to the deck on the short ferry crossing). Apart from (an admittedly exceptionally good) coffee from the sleeper attendant in the morning, that is. But a slap-up meal in the evening at Milan station before boarding, plus a traditional long-distance-train picnic bag which was enough for a hearty breakfast while running down the coast on the way to the ferry the next morning, did the trick.
A warning - the first cafe I dived into right outside Syracuse station on arrival, prior to heading to my hotel, made a clumsy attempt at ripping me off. My Italian isn't great, but it's good enough to argue about arithmetic; he lost the tip he'd otherwise have had and so ended up worse off.
Re booking windows: the sleeper is I guess an ICN (certainly not a "HS" train), but I'm pretty sure there was no problem booking months ahead. (Maybe their booking window is longer than the day-time ICs?) By booking well ahead, I managed the journey from London to Paris, plus Paris to Milan, plus the bed from Milan to Syracuse, for little more than £100 per person end to end. Though I guess it's a bit more these days, especially the London-Paris bit!
In terms of journey times and the slow train crossing on the ferry referred to above (by someone suggesting it's quicker to get a train to the port and then cross as a foot passenger) - I read somewhere about plans to speed up long-distance rail links to the island. Apparently they'll be building short 4-carriage (including the driving cab at each end) HS sets - I think as sleepers too - which will run from northern Italy to Sicily. That way they can double them up, run as 8-coach trains via the HS lines where they exist (so cutting quite a bit off of the journey time going the length of the country),
and can then divide them into the 4-car units at the port [to be short enough to get in the ferry] and drive them on and off the ferry under their own steam (presumably they'll have enough battery back-up for that), so avoiding the lengthy shunting (especially on the mainland side) which goes on at present - which takes far longer than the actual ferry transit time itself. The shunting on the Sicily side seems quicker because the train stays in bits to run to different destinations, and I think there's no reversal at the dockside as there is on the mainland.
A much fast sleeper the length of Italy does sound tempting... It could mean London-Sicily in not massively more than 24 hours, leaving one morning, being on the island the next morning.
