an LM386 op-amp (Many are available, including RadioShack part #276-1731 and Digi-Key part #LM386N-3-ND.)

a red LED

an 8-pin IC socket

an 8 ohm speaker

a 100 μF capacitor

a 1/4″ mono phone jack (a guitar jack)

a 10k ohm variable resistor (Variable resistors are also called potentiometers or pots, and in this case you want an audio taper; see Audio Tapers vs. Linear Tapers in Building It.)

a control knob cover, such as RadioShack part #274-415

a 470 ohm resistor (coded with yellow-purple-brown stripes)

a DPST toggle switch (This can be a little hard to find, but can easily be replaced with a DPDT switch like RadioShack part #275-666; it’s pricey and far beefier than the project calls for but is also easy to install and looks great. For a full discussion of toggle switches, see Types of Switches in Building It.)

a 9-volt battery clip

a 9-volt battery

24-gauge insulated wire, either stranded or solid-core

22- or 24-gauge bare bus wire (This is uninsulated solid-core wire; the 22-gauge is slightly thicker than the 24-gauge and thus preferable.)

whatever enclosure you choose (A cigar box is nice; hint hint.)