The best bottles of beer are not screw offs. So, if you plan on drinking some beer, it is a good idea to have a bottle opener. But, what do you do when you cannot find one?
You go beer Macgver on it!
There are hundreds of videos on Youtube devoted to alternative ways of opening your beer. A lot of them are bad ideas. Don't use a chain-saw. Don't use an iPhone. Don't use a knife. Don't use the kitchen counter. They are all bad ideas.
The classic method is a lighter. Apparently, lots of beer drinkers also smoke (or are fans of fire).
Paper products also work. Consider a sheet of paper or a napkin.
Keeping a bottle opener on a key-chain is a good idea, but if you fail at that, consider a carabiner or a key.
Try a pen. Although, I can never find a pen.
Try another beer.
What else you got?