The dessert package is $59/person (at least it was the last time we went). It includes a box of crackers, cheeses, grapes, and quite a few desserts. You also get unlimited non-alcoholic drinks.
You can call 1 month in advance to get tickets. On the day of the reservation, you pick up your tickets. When we were there, we picked ours up at the Guided Tours window. They tell you to line up at the podium near the show at around 8:00PM to choose your seat. We always show up before that, as the line forms early. After you choose your seat, you're free to leave and come back 15 minutes before the show. Keep in mind the area gets very crowded, so you might want to stick around in your seat if you are going to the first show.
Have fun!