Not sure caterers will be helpful since they're paid for what they bring to the party and they don't care at all whether it gets eaten or not. Similarly, the all-you-can-eat buffets have lots of data from which to estimate how much an average customer eats, and they have the law of large numbers on their side, too.

For the house parties the usual answer is just experience. After a few missteps most people can learn to have a workable idea of the amount of food needed without formulating a full Bayesian model or even without a simple spreadsheet. Of course there is some uncertainty and the incentives make the host provide the amount at the top end of the reasonable estimate interval.