When I booked a sleeper car for my 16-hour Amtrak ride, I could choose a roomette, bedroom, bedroom suite, or accessible bedroom. I went with the roomette, which was the smallest sleeping accommodation so I assumed I wouldn't have much space for luggage.
Larger luggage can be checked when boarding or stored on the first floor of the sleeper car in case you need to access it. With that in mind, I packed one rolling carry-on-sized bag and a smaller piece of luggage that could fit under a seat on a plane. I packed everything I'd need with me in my room in the smaller bag, including snacks, entertainment devices, toiletries, and clothes for sleeping.
I put everything else I needed in Sacramento in a larger bag. I ended up having space to keep both bags in my room but I was still glad to have everything organized and in one place.