Step 2: Step two: electronics
it's a good idea to test the circuit first out on breadboard if you have it.
note that this circuit is quite stripped down and only makes the guitar's signal an overdriven tone (distortion)
you could add your own version ex: like the little gem amp, but keep in mind you'd have to add potentiometers and there's not much space inside the tin for that
you can use an allegator clip to a guitar wire for testing rather than soldering to the jack before you put it in the tin
cut out a piece of perf board so that it will fit inside the tin ( allow some extra room for batteries)
solder it on to the perf board but add wire so you can connect it to the switch, jack, speaker and batteries
i've added a picture of how it might look on a breadboard and perf board
the yellow wire recieves the guitar signal
the green wire goes to one side of a speaker
the blue wire goes to the switch
the 9v clip is just to signify power in and ground
you can see that there is not much there, and you'll only need one or two hole spaces surrounding your LM386 chip when soldering it onto perf board (so about an 8x8 hole board)
make sure all ground connections are well soldered together, and you may need to have a wire touching the jack's ground (sheith) for a better sound.