Amtrak used to sell blankets, and before that they used to give them to passengers. I don't know if they still sell them.
In anycase, there is fantastic lounge onboard called the Sightseer lounge. Its the closet Amtrak comes to offering a dome car, and technically it is a form of dome car. You can get spectacular views from it, and I suggest strongly that you take advantage of it. You can also buy snacks, as well as both soft and hard beverages, from a snack bar on the lower floor of that car. Further, I also suggest you take advantage of the Dining Car which offers diner-style meals that, frankly, range from ok to pretty darned good. The dining car is not particularly cheap, although I wouldn't call it overpriced, either.
Check out this topic
for an idea of the kind of food and quality of it. If you book a sleeper, you will get your meals included for all three passengers, but only pay one upgrade fee, which is why I personally think its a good deal.
Lastly, trains are a very social place, especially compared to a plane. Take advantage of it. I've met some pretty good, long term friends onboard Amtrak trains.