We've been invited to an autumn potluck, and the invitation says to "bring enough for everyone." There are going to be 30 people there, however. How much food do I need to bring?
The standard rule is to bring enough to feed the people in your own group, plus a little extra, but that can vary. If you're one of only two parties bringing an entree, for instance, you're going to need more. You should ask the host for specifics in advance.
And remember that there are important but little-known exceptions. If you're bringing Polynesian meatballs, Mars Bar squares, devils on horseback, or ambrosia salad, consider making extra, because as much as the other, cooler guests might mock you, they'll eat it, and then they'll slink back to the table for seconds. If your go-to potluck dish contains a can of mushroom soup, on the other hand, I'm sure nobody will mind if you bring only enough for yourself.