In all honestly, the Fantasmic package seating is not so great. Most times, it is off to the sides of the theater.
I would much prefer to arrive ahead of time, pick a seat, have someone stay there and then go get a counter service meal to take back to the theater. There is a small snack shop at the Fantasmic theater. I believe they sold churros, hot dogs, pretzels and turkey legs. Right near the entrance to the Fantasmic theater are several places you can buy hot dogs, pizza, burgers, etc. We did this for years and years.
Last year, we booked a dinner at the Sci-Fi at 7:30 p.m., ate our dinner and headed over to the Fantasmic theater. Had plenty of time for the late showing. We are planning on doing the same thing this June.