Goldilocks…………………..
You can ask and ask and ask that guest not bring any food or gift, BUT people who were brought up properly do not arrive empty handed.
Thus, we tell them the menu is set, the cooking is done, but it would be very helpful if you could pick up a bag of ice. They feel they are both bringing something, helping us out, in that we don’t have to leave preparations and go shop erev Yuntif/Shabbos.
And we never have to explain that we eat this hecksher and not that, or from this bakery and not that. Or even worse, the home you think is kosher isn’t up to our standards.