I have used the Indian Pacific and the Ghan back in 2005.
There have been some changes since, according to the site of the man in seat 61, so I checked the details to make sure I give you the right information.
When I used it, I had a seat in a sit-up carriage, these days those are not sold anymore, so you will need to buy a more expensive ticket, which does include things which the people like us had to buy.
Even the Red service sleeper cars no longer run.
Which is included in the price depends on the service you pay for.
Leaving from Sydney, you will arrive in Broken Hill in time for an early breakfast or you can use the trip (if available, not sure from the seat 61 page.) It is a small town close enough to the station that it is no hardship to walk in and have a good look.
That same day you arrive in Adelaide mid afternoon, and there is a city tour ready for the ongoing passengers, I though it worth the money back then.
Next you will be on the train for the next 20 hours or so, to have a 2:40 stop in Rawlinna. I am not sure whether I did stop there, back then, as I do not remember the name. But I do remember walking around on at least one more stop after Adelaide.
I had a fairly long delay, 10 hours or so, but the time table I find online does not match the one I remember, so I can not be sure.
It was a very long sit, it is better to have a bed, but you pay for the service.
Back then most people seemed to travel with their car, the car transporter train cars were filled to capacity and the train tickets (with the beds) came as part of the package for those people. Maybe a good plan if you want to travel only one way long distance.
Traveling the other way you will have the same kind of stops, but at different times of day, as suits the trains schedule.
The Ghan also has several stops where you can join a tour. And also does no longer has the Red service seats and sleepers, which makes my experience out of date.
But the places mentioned in the time table are ones I do remember, if not from the train ride. (I think there are now longer stops than when I used the service.)
As mentioned in the comments on the question, the train mentions the 'more common' food restrictions which they can accommodate, those include vegetarian.
What I remember is that the food service was good, included in the more expensive tickets (which are now the only ones available.)
You will still need to contact the train company when you are going to travel with them, so they can make sure they do have enough supplies for you.
If you want to spend less, there are other trains in Australia, which do have cheaper options. The Seat 61 site has several listed. I have not used those yet, as the rest of my travels were by tours (6 days each, 12 seat buses,) and flights.
The two trains I mentioned run coast to coast, one east-west, the other north-south. And with that unique position they can charge more per passenger (who are mostly tourists or in need of car transport) than trains along the coasts which have to compete with car and coach travel.
All being said, it was worth a lot to do those travels, but I doubt I would be able to afford it on today's prices, and you will have to be a train buff or a rich person to want to spend the money.
With the time table, trains running once a week, I do not think you will want to hop off and wait for the next train unless you want to do sight seeing in the area or have a good reason to visit and stay for one or two weeks. You will have to buy two (or more) tickets in that case, which will likely work out more expensive but I have not done the calculations for you.