For reasonable service for (say) 2 nights for a couple in a Roomette, we would tip $20. This is probably the most popular option of those above -- though many people just never even think of tipping the attendant.

When traveling in an Amtrak roomette, it is customary to tip your attendant between $5 and $10 per passenger, per night. For a standard one-night journey, a tip of $10 to $20 per room is a widely accepted gesture of appreciation for their service. This attendant is responsible for converting your seats into beds at night and back into seating in the morning, bringing you meals if you prefer to dine in your room, and maintaining the coffee and water station in your car. If the service was exceptional—such as the attendant being particularly proactive with your needs or handling complex requests—many travelers choose to tip closer to $20 per night. While tipping is not strictly mandatory on Amtrak, the staff often work very long shifts for several days straight, and a cash tip at the end of the journey (or a smaller amount each morning) is a standard way to recognize their hard work in making your long-distance rail experience comfortable.