Here's something new I just came across: a mezonos cover. What on earth could that be?
First, to get on the same page, we have to remind readers what a challah cover is for. When you sit down to eat and drink, and have several blessings to recite over different types of foods and beverages, halacha proscribes the proper order: Hamotzi, Borei Minei Mezonot, Borei Pri HaGafen, Borei Pri Ha'etz, Borei Pri Ha'adama and finally, Sh'hakol. So when we sit down at the Shabbat table, we should really start with Hamotzi, but since we need to officially sanctify the Sabbat over a cup of wine first, the order of the first two blessings gets switched.
The Sages were sensitive even to the "feelings" of inanimate objects, therefore we cover the bread to spare it the "embarrassment" of being consigned to second fiddle.
Well, when you recite Kiddush in the morning, if you serve on cake and cookies and kugel, etc., without breaking bread, the same mechanics come into play, i.e. Borei Minei Mezonos should come before HaGafen, and since that is not a possibility, we cover the mezonot.
These Mezonot Coves are designed for public kiddushes for the congregation, after a bris on Shabbos, etc.
Many people are not familiar with this halacha, but those who are aware of the issue will quietly lay a napkin over the plates of cakes and cookies until after someone says Kiddush.
I doubt whether you really need to cover all the mezonot on all the tables at a large Kiddush, rather the table where Kiddush is recited should suffice -- but I could easily be wrong on that.