I had the idea for this fashion accessory when i found a lighter with a little flashlight built in. The only important part was the battery holder for 3 button cells. I also found a couple of LEDs and a little switch in my "parts and pieces" drawer. Little wires are not hard to find anyway.
I did some calculating and everything should work out fine without the need of a resistor. I just assumed that I grabbed the average LED with ~3.1V and about 20mA, so 3 batteries with 1.2V each would add up to 3.6 which is not too much for the LEDs and according to the data sheet 1 battery should be good for 160mAh or about 4 hours continuous work, right? (I know I will hear from you if I got it wrong.)
The whole thing was done in less than an hour so I moved on to creating the body.
Please use this for your own creation: LED calculator