I never bought one of the Kellogg's packs and neither did any of my friends. I did complete my 1971 set after buying many packs at Kresge.
A few of these might be impossible, but I might as well have something to search for when I go to the National each year. Otherwise, I just end up spending money on stuff that I don't really collect. Searching the show won't cost much because I'm too cheap to pay the big money that will be required at the National for something like this.