My guess for the Silver Star(if riding the Cardinal earlier this year and seeing the Card's cafe menu, is any indication what it probably will be like on the Star), is that the cafe car menu will probably be the same menu between both long distance trains:
https://www.amtrak.com/content/dam/...ational/National-CafeCar-Menu-Amtrak-0617.pdf
And back to my experience when I rode the Cardinal this year, there is a VERY likely chance they will run out of food earlier than you might think on the Star's run, in whichever direction(s) you're traveling. Like I did before riding the Cardinal(and I'm SO THANKFUL I did this myself), I'd get a really good meal somewhere before your board the Star, bring some leftovers onto the train, and eat your leftovers from that meal onboard the train. Also bring some other snacks to help tide you over if you get hungry easily(like I do), such as granola bars(this is what I typically bring), fruit smoothies(I usually bring one, either a Naked or Bolthouse Farms smoothie), or other similar nonperishable snacks(i.e. Goldfish crackers, cereal, anything) to help tide you over for how long train trips can feel like for their length. After all, there is a good reason this train is nicknamed the Silver Starvation(no dining car), sadly to say.
I'll let the other posters respond and properly fill in, whether Amtrak is planning very soon to add flex dining to this train. I think someone else(maybe PennyK? can't remember exactly who mentioned that rumor) said flex dining is coming to this train in early 2020, but not sure when it's scheduled to begin.