Step 1: Get the parts:
2. Old wall/car charger that fits your cell phone.
3. Male USB.
4. 220 ohm resistor (red-red-brown).
5. LED (color is up to you).
6. Power Switch.
7. USB extension cable (just in case you can't fit the USB plug directly into your computer).
Step 2: Connect the dots...
Step 3: Jam the crap in there.
Cut, or drill the hole in the lid for the LED. Once you wedge that in, glue it in also.
Same deal for the power switch, and cord exiting going to your phone. Dont be bashful with the glue/filler, cause the most secure everything is, the longer it'll last.