friend is leverage.
so long as you have something nearby that is sturdy (most likely metal), you can easily grip and has an edge to it, you can probably use it to remove the cap from your bottle. just place the edge of the object under the lip of the crown cap and pry away slowly. it's almost always going to take more time and effort than a device that was designed specifically to open bottles, but it's not rocket science. work your way around the cap as you pry, and the cap will eventually release.
a house key will certainly work. it's typically thin enough to place under the lip of 