The X method seems to be the best way if a sak of P-38 is not available. I used to take along some V-8 juice on camp outs, and I would use the sheepsfoot blade on my stockman to open it the can. I would lay the sheepsfoot blade on the top of the can edge down in contact with the metal, and the blade kick on the rim of the can. Then firmly press down on the tip of the sheepsfoot, and cut through the can lid on an angle to the rim. Repeat with the blade tip on the start of the prievious cut and you end up with a triangle hole like a church key would make.
Now it seems like alot of cans are pull tab open, sardines, V-8, Cambell soups, even Spam. Modern kids have it easy.