Take a lumbar pillow if you have lower back problems, like most public transportation, the seats have very little lower back support for long rides. You buy a pass for one or more regions and have great flexibility in your train travel within those regions. Typically you can stop over several times at different cities as you travel. This lets you take in attractions for as many days as you wish on your trips The North American Rail pass allows you to travel anywhere Amtrak or Canada's Via Rail go for 30 days of unlimited travel. Since VIA's route include the breathtaking Canadian Rockies resorts and a series of resort hotels built in the late 1800's and early 1900s exclusively for rail passengers, this rail pass is a great opportunity to see hidden Canada.
Most fares have discounts available.
Off-peak is typically fall through spring. Point to Point fares not otherwise discounted have some sort of mysterious discount program that operates as a function of time. You can tell this by going to the Amtrak site and putting in the same trip at different times of the week and different times of a given season and you'll get different total prices. I've asked several Amtrak employees to explain these to me, but no one seems to know. Generally, the later you book on a nearly empty train, the cheaper the seats will be.