all you need is a cap you don't mind poking a hole in, a pocket flashlight with clip and a small knife
Step 1: Poking Holes!
mark a line in the centre about a half inch from the crown and stab it (careful!!)
Step 2: Adding the Flashlight
now grab your trusty flashlight and thread the clip through the hole
Step 3: Done!
and there you have it a free and easy solution to hands free lighting!
I'm not sure that this is the first ever instructable for this solution, if it is, great, if not, sorry I didn't know.
either way this is a great fix if you don't have a separate headlamp.