Have you been to an amusement park or concert lately? What I’ve now experienced twice this year were topless drinks when purchased from the concession stand (vs. a vending machine). It’s extremely annoying when you go by yourself to purchase drinks for many or food and drinks for two so you don’t lose your seat.
But someone should come up with a reusable cap for plastic soda bottle, for beer bottles, even for cups (more difficult due to random sizes). There is already a great product for cans.
Or you should just bring a cap or two with you when you go to a concert.