Wiring leds for a prop

You'll want to make series chains of 3 LEDs each, equaling 12v each. These chains can then be wired together in parallel. You shouldn't need a resistor if using this method.
 
LEDs are constant-current devices. Relying on the battery's internal resistance to limit current is a bad idea; that's why so many of the "9-led, 3AAA" flashlights have dead LEDs... I would always us use a resistor or other current-limiter in anything other than a throwie/spike marker with a CR2016 battery.

/mike
 
I'd be wiring pairs in series with a resistor.
80 ohms for the rated 30mA forward current.
Increase the resistance if it's too bright or you need better battery life.

I'd guesstimate that with 6 leds at 30mA, you're probably looking at totally killing a battery in 5 or 6 hours, noting brightness will have decreased significantly towards the end of that...
 

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