What we're doing here is combining a standby switch (aka a silent switch) and a kill switch, only with a twist.  See, a conventional kill switch only cuts the signal when pressed.  However, some readers of this site have requested an option by which the switch could be used in the opposite fashion.  In other words, what if the guitar was silent except when the button was pressed?  Musically this presents some new options, but it also makes the guitar difficult to operate if you aren't actively pressing the momentary push-button to allow the signal to pass through it, and who wants to play like that most of the time?

What we're going to do here is have a SPST in the circuit that by default throws the signal to a "normally open" push-button switch.  At this point, we have effectively created a standby switch for the guitar.  When the signal is sent to the push-button, the signal will be cut... but only until the push button is pressed.  You now have both options available to you.

You'll need a SPDT* to function as a standby switch.  In this case we aren't cutting the signal so much as re-routing it to the push-button.

*A DPDT will work as well if you have one of those or a push-pull pot lying around.

As mentioned above, you will need a "normally-open" push-button switch.  A normally-closed switch would allow the signal through unless it is pressed.  If you installed that, the "standby" switch wouldn't accomplish anything without the button also being pressed, so it would be redundant.