I hate to see a question go unanswered, so I will tell you what I know, although I can't answer your question completely.
From what I have observed, the Chuckwagon is open when the campfire activity begins (6:30 during standard time; 7:30 during daylight savings time), and remains open until the end of the movie (around 9:00 during standard time; 10:00 during daylight savings time). On Fridays and Saturdays during standard time, they show a second movie, so it may stay open until 10 then as well.
As far as the "menu" goes, I can't tell you everything, but it is pretty limited. Hot dogs, microwave personal pizza (Tombstone brand), popcorn, ice cream, soft drinks, beer, candy, marshmallows and smore kits, and that is about it.
TCD