Replace the bulb in a 2xAA mag-lite with a bright white led. A cool burning led will give you longer battery life and won't burn your face off.
Step 1: Collect the parts
You'll need a 3.2 volt LED -- I think most bright white LEDs qualify. A ruler or caliper. An old, beat-up mag-lite, the kind that takes 2 AA batteries. Some wire cutters. A low speed or variable speed drill and 1/4" bit (not pictured). A small vice or pair of adjustable, locking (vice-grip style) pliers will come in handy (not pictured).