I love to collect examples of bizarre pairs of goods that sellers or buyers apparently believe are complements or substitutes.
Our local, now-defunct Tower Records used to have condoms for sale at the check-out counter, presumably in the probably reasonable belief that they and rock music are complements in students’ consumption.
Near my apartment in Germany this summer, a funeral home has a casket in the window, with seashells on top, sand strewn around, and a seagull perched atop a cross. Do the owners really believe that customers will be consuming funerals and beach vacations together? I wonder.
I disgust my introductory economics students by listing peanut butter and mayonnaise as complements, since I used to make myself sandwiches of these two items when I was in college.
Any other amusingly bizarre real-world examples like these are most welcome, the weirder the better.