Miss Manners: The rain changed our plans and shed light on a potential problem

Dear Miss Manners: I know the etiquette of the host paying for the event, not the guest. Which is great. However, in my wide circle of friends, we do things differently. We often eat potluck, though when one of us does provide the meal, we provide all of it at our own cost. Guest will usually bring wine to share, or maybe a homemade dessert if they want (and if the host agrees).