If you are riding on the Coast Starlight you will be riding on a very beautiful double decker kind of train. As a "model" name that kind of equipment is called "Superliner"---that is the name of the type of equipment, not the name of the train.
I assume for such a short trip you are riding in daylight hours. You will find the coach seats quite large and comfy compared with airline coach. First class, on a train, mean private rooms in what is called a sleeping car.
Train food is usually quite good, sometimes a little expensive. But it is a neat treat to sit on a train diner(esp. the second floor, as you will be on the Coast Starlight) andf watch the scenery go by. Are you traveling alone or with others? If alone, or with no more than two others you will probalby be seated with strangers in the dining car(assuming you are traveling at meal hours). It can be very enjoyable to converse with (usually pleasnat) strangers on the train. It is often more sociable than other types of travel(but don't feel forced to be sociable ).
Basically, just relax. On boarding you may be told where to sit, sometimes not. Seats are "reserved" in a sense, but not individually assigned, not, at least sometimes, until you get there.
Whehter you eat or not, you will find a beautiful double deck lounge car for sightseeing. It has food service downstairs, snack type foods, less filling and less expensive than dining car food. A good thing to do is sit in the upstairs seats and watch the scenery. Some of the seats are turned straight toward the window, various patterns. Unlike what you see on anything else other than a cruise ship.
Trains hae ample restroom facilities. ON a double deck train like yours, most of them are downstairs.
You may want to store any big luggage downstairs, rather than lugging it up the steps. Take lighter luggage upstairs with you. And, of course, it can be checked, except at some very small stations.
