This is what I see as on-train meal opportunities during the 8-day official Fest. We usually eat together for lunch and dinner, and are on our own for breakfast, with perhaps smaller sub-groups for earlybirds and later sleepers.
Saturday, 7/15: Dinner aboard Train #3 Southwest Chief
Sunday, 7/16: Dinner aboard Train #316 Missouri River Runner
Monday, 7/17: My guess is that if Train #21 Texas Eagle is running on time (7:55 PM departure), a late dinner might be offered. However there is plenty of time in St. Louis to have dinner while in town.
Tuesday, 7/18: Breakfast aboard Train #21 Texas Eagle. Scheduled arrival before lunchtime.
Thursday, 7/20: Dinner aboard Train #22 Texas Eagle.
Friday, 7/21: Breakfast aboard Train #22 Texas Eagle. With a 1:52 PM scheduled Chicago arrival, maybe lunch too.