The Magic Kingdom was so crowded for the first showing of Wishes that, 2 hours ahead of time, many of the best viewing spots were already filled. The family in front of me had been waiting (in a very prime location) since noon! When you plan for Disney events, time takes on a new meaning; 'arrive early' can mean 'arrive 2 hours early', so plan accordingly.
Fantasmic does have a special viewing area for Dinner Package holders, but be aware that everyone in your party will be required to order a full meal at the restaurant. Another option is to get in line and have one person in your party stop at Sunset Ranch Market (an area just outside the Fantasmic ampitheater that has various counter service stands) and pick up dinner there. You can eat while waiting in line, which takes up some of the time you'll spend waiting. There IS food inside the theater but it is very limited.
Enjoy!