Traveling by train is a comfortable, affordable way to see more of the country while you're getting to where you're going.
The main objective is to control your environment as much as possible. That means you'll need ways to regulate your hunger, body temperature, and senses of smell, touch, sight, and sound.
Most of the following suggestions are common sense / what you'd want to do for any kind of long trip, but it helps to have a checklist:
Sit far from the bathrooms. And anyone who seems crazy because they will be too chatty. If you train has a viewing car, camp out there. Stretch every few hours. On long distance Amtrak trains there are leg rests that extend from under the seat; look for the black knob on the arm rest (it looks like a joystick) that you can pull back.