For the ones who ask, if you want them to bring something, you make a specific suggestion or just let them know what you haven't picked up yet and let them choose from that list. You are not responsible for somebody else's what-if and shoulda-woulda-coulda issues. If they are interested in bringing something, they'll ask. Otherwise, they won't. If they're battling it out in their own minds thinking that they probably should or should not have asked, then that is their issue, and they'll know for next time. You can't do all the emotional work for everybody.
Maybe it depends on the event. When I have a party, I usually provide everything, though I'll encourage them to bring any speicifc beverage selections that they prefer. My bar is stocked, and the food is usually a good balance, but I am not offended if somebody decides to leave my house and make a run to the store for a particular fix.
I prefer telling them what I need than to have them bring something that I don't want and expect it to be added to my thought-out menu.