Zebralight SC62 is very small 4", 1000 lumens bright, with a good clip, and useful low and medium modes, $85.
Regardless, you should get a light that uses an 18650 3400mAh Lithium Ion battery, 2 x $20.
A good charger is the Nitecore i4, $20.
It's the one all the way on the right. That is small.