Simple Flashlight, just need one 3mm Straw Hat White LED Lamp Light Emitting 3V DC Diode and one 3V button cell "CR2016L". They are available at Amazon.

NO SOLDERING! Easy to assemble.

This has a lot of critical tolerances.
1.) Clean print.
2.) The shorter wire of the diode is negative. Trim that so it fits in the recess on the bottom half of the case.
3.) Trim the other positive lead so it 1/8th of an inch past the center of the battery.
4.) Add the button battery (CR2016L) between the two leads with the positive side facing up. Push battery into case recess.
5.) Position the leads of the diode so they are perpendicular to the case and add a small drop of superglue to the head of the diode. Hold firmly in place with needle nose pliers until glue sets.
6.) Add a small piece of tape to the end of the battery so the positive lead of the diode does not make contact with the edge of the battery.
7.) Ream holes so they are larger. (Just enough to allow the posts from the other side to snugly fit. If you ream too much the posts will not lock in place.)
8.) Snap the sides of the case together.

Note: If you want a tighter fit with no seams, you can glue seams and use pliers to clamp edge of sides tight. (Glue and clamp just the outer edges. DO NOT glue and clamp near the center of the case.)