Yes, you can bring food on Amtrak trains that you can eat at your seat or in the Superliner sightseer lounge if that is available on your train. We encourage bringing food on board, including to-go meals from restaurants near stations, if you have special diet needs, like to eat large amounts of fresh fruit and vegetables or don’t want to purchase food in the cafe or dining car (note that meals are included if you book sleeping accommodations). A small cooler can count as one of your carry-on items if you need to keep anything refrigerated.
Amtrak does have the restriction that if you are buying food on board the train, you need to eat that food where you purchased it, such as in the cafe or dining car. Alcohol can also be brought on board if you have private sleeping accommodations, as that is the only place you can consume it, and not publicly in coach seating.