We have only done this on the
Disney Dining Plan (the regular plan that includes 1 table service per night.)
At Hollywood & Vine, it's a buffet so you just do the buffet. At Mama Melrose, you get an appetiser, entree, dessert & beverage (this is the only place you get an appetiser for 1 table service.) You choose any app, any entree & any dessert. Beverage is coffee, tea, or soda. At Brown Derby, it costs you 2 table service credits (because it's a signature restaurant.) Again, you can choose what you want from the menu (not a set meal.)
If you're paying cash for your meals I believe H & V and Mama Melrose are a set price for the Fantasmic Package. You will be charged $10 per person if you cancel less than 24 hours ahead of time (or are a no-show) so they do take a credit card number when you reserve. The packages are very, very popular and they only offer a limited number of them so they book up fast. People report calling on their 90 day mark and having both H&V and Mama Melrose being sold old early in the morning.
The meal times are generally fairly early...in the 3:00-5:30 range; one reason for that is to make sure you're done in plenty of time to get to the showing. They used to say you could show up with your reserved seating card at 30-45 minutes before the show, but I believe people are now saying you better get there 60 minutes ahead because the crowds are so big they can't hold the reserved section as long as they used to...