you dont need special tools, casing,switch,etc.
its simple and quick project that you can make just following this steps :D
Step 1: Parts
1x LED ( any color,white is brightest)
1x cr2032 battery ( 3v battery, button cell)
some glue from glue gun
Step 2: Building
than put anode of LED to positive side of battery. Put peace of glue on anode and start heat it with lighter ( for 2-3 s) . when you melted glue just ake scalpel and push it so that glue can stick to battery.
Step 3: Finish
when you want to use it just push cathode to - end of battery and light comes....
one note, my LED is glowing ok but battery is half discharged ( i scrap 50 batterys from old motherboards so half of them are discharged and half is around 2.8 v )
this flashlight can work as mouch as led throwie (1-2 weeks constant, or on daily use from bed to bathroom = 1 year)