Swag. Set up some shitty designs on one of those dropshipping sites and a storefront. Mugs, hoodies, etc.
One time I experienced a "trending topic" first (or second)hand; the app we were building accidentally sent a pair of test notifications to 2-3 million people, first the test message, then a second saying "zodat Hajo het ook gelooft" (so that Hajo (name) believes it too). That took the daytime internet by storm; news articles, radio segments, twitter trending topic, etc.
I mainly followed the topic on Twitter, and before long there were adverts on there selling swag related to the trending topic. There's companies (or even bots?) scanning Twitter, making swag-on-demand for trending topics.