Grab the datasheet for your LEDs and open Circuit Playground... find the values for 'Forward Voltage' and 'Forward Current.'
Plug-em' in, and voila!
It looks like the LEDs I selected require a 1/8 watt 180 Ohm resistor to prevent the battery from over-driving the LEDs and burning them out.
There can be a little variance in the resistor value... +/- 10% shouldn't be a problem.
Just remeber to enter 3x for the Series LED Count!
You can even free-wire the circuit if you want... my prototype may be ugly, but it works a treat!
I sealed the prototype in epoxy to prevent the connectors from wiggling around. Some of the epoxy ran through the holes in the clip... next time I'll plug those with a bit of hot-glue.