Another of many votes for LUNCH. For me - it's about the Pot Roast entree. I've never had room to try that dessert!
I'd also try a different plan for the day - depending on how much you are paying to get into the park before the party. When I had an annual pass - I'd book a very late lunch in the park - like 2-2:30 - and have that be the FIRST thing I was doing in the park on the day of a party. So arrive at 2 to stay through the party. Then have 3 FP+ after my lunch but before the party starts.
Now obviously - since you can get into a party with a party ticket at 4 pm - you don't want to spend two hours on a park day ticket if you have just a 3-4 day ticket overall.
But - starting early and taking a break and coming back works, too. But me - I'd want to arrive at the party no later than 4:30. And realize that DURING the party - there's very little open for food - so you need to get dinner before 7 pm. Lots of people enter around 4 pm and plan to eat before 7 pm at the counter service places - so they are busy. Not ridiculously busy - but not empty!