When it comes to things to have always in your kit, a good headlamp is one of those things you better get right.
I've used several over the years and I keep on coming back to this one, the Petzl Tactikka+.
Light weight, compact and with a good battery life, the Petzl Tactikka+ lives on one of the pouches on my vest, or on my ruck all the time. The fact that you can have a red LED light for preserving night adapted vision, and 160 lumens of white LED light when you need illumination, in a very light and comfortable package, it's great.
According to Petzl, run time is about 2 hours on white light high; and 100 hours on low. WIth the red light mode, I found it to be more like 4 hours on high. I haven't tried the white mode beyond the low setting.
Fairly water resistant, I was submerged under water with it for a few seconds and it was still working after it.
Head band is a wide elastic (multicam in this case) that can be adjusted. I found it very comfortable and it can expand to fit on top of a helmet. The casing can be rotated up or down, so you can point the light to a map, or avoid blinding a team member.
For storage I bought the pouch from Petzel, and while not the best out there, it's a nice way to store the light.
Yes, this light is now part of the default kit. It goes everywhere. Highly recommended.