Plastic corks work great. The multiple flanges give a good seal and are easy to insert. I've never had to purchase any, just reuse the ones I've collected over the years.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk