Stick all the way. Preferably something like a 5-6' hazel sapling. It really works, doesn't require fine motor skills like a gun, doesn't raise any eyebrows and can be used as a non-lethal deterrent if possible. If there is no other way a quick blow pretty much anywhere along the body will snap the spine instantly. Follow up with a coup de grace - crush the head.

Sounds brutal and it is but that's life. One should avoid killing wildlife if at all possible but if you have no choice a stout stick is a good defense against a snake.