[thatcat]

You can use the flat edge of anything with a little leverage to pry a bottle cap off using your fingers as a fulcrum beneath the cap.

https://www.youtube.com/watch?v=rm0ZkABVqjQ

[roel_v]

Real men use their teeth though.

(I never opened a bottle that way; but I did see someone break a tooth once. A molar, clean in half. Not sure if I'd rather have a wire stuck in my gut or break a molar in half.)

[david-given]

I have opened beer bottles with my belt buckle. Apparently this surprised people.

...I have seen someone successfully open a wine bottle with a shoe.

[kozak]

Cap of another (unopened) bottle works perfectly for this.

[stephenr]

if you have sturdy (ie like volkswagen/audi/bmw) keys, you can use a key in a similar fashion

[eric_h]

Bic lighters are exceptionally good for this (one of the important life skills I learned in college).

[shiggerino]

Can't speak for BMW keys, but every VAG key I've had has been horribly flimsy. Don't use it to open bottles or you'll be locked out of your car.