Couch Gag: It's a spoof of the hidden dinosaur game in Google Chrome when you are offline. The Simpsons jump over cactuses. Home gets caught on the last cactus as the rest of the Simpsons make it on to the couch.
At the end of the episode, when the group of conspiracy theorists are throwing out various ideas, Marge mentions a cartoon that can predict the future that they should watch. This is almost certainly a reference to a Facebook meme that points out several instances where The Simpsons accurately predicted the future, including the creation of the iPod, the attacks of 9/11 and the presidency of Donald trump, among other things.
The characters voting against Springfield ceasing its Columbus Day celebrations are all the Simpsons characters who could conceivably have Italian ancestry. Christopher Columbus was Italian.