As far as group events like a church dinner, if this is happening repeatedly, maybe the organization which is hosting this dinner needs to look into doing something different. Maybe catering the dinner and charging an entry fee. Or having a set group of members provide all the food and get reimbursed.
This happened at the church we went to while I was growing up. For years, the protocol was that a group of church ladies would prepare a meat dish for everyone. You came with a side dish or dessert to share, and brought your own plates and utensils. Cups would be provided for drinks. After you put your stuff at your seats, you would get in line. At the appointed time, the minister would say grace and the line would progress through the buffet. Desserts were cut up in the kitchen and served after the dinner was finished.
There was one family (it's always that one family, isn't it?) who took this to the extreme and ended up changing the protocol. They would come super early and bring these enormous plates. These were the kind that had multiple sections. And they were HUGE. The family would take their places at the head of the line and wait the hour or so it took until the appointed dinner time. Then they would load up on their trip, with mounds and mounds of food on their huge plates.
One night there was literally no non-dessert food left for the people in the back of the line. As in, no meat left and all side dishes scraped clean by earlier people who were desperate. Apologies were issued and the protocol was changed immediately. After that, all tables were numbered and they would draw numbers for which table would go next. Mostly they'd get kids to draw the numbers and you would get teased if you drew your own table's number, especially if it was early
Then there's the story of the incredibly stupid caterer who agreed to provide the banquet dinner for 3500 hungry orienteers at the World Masters championships back in 1997. Who also decided that they could do that banquet and another at the same time, because they don't really need that much food, right? I think the reports were that about 1500 people paid $35 to only have the leftover butter pats.