I've done several things. Once I met a group of people at the Liberty Tree Tavern (back when the characters dressed up) and we finished up right as the party was starting. I've also done a meal at O'hana, again finishing up about 6:30 and heading into the start of the party. I've also done the quick counter service earlier in the park and had a snack in my bag for later. Lots of options depending on your own preferences. Like Tricia, I don't like to waste official party time eating!