Something you'll want to pay attention to with battery headlights and power banks alike is charge time: with a multi-day brevet, you could get into a situation where you don't have enough time to fully recharge your gadgets overnight.
Having a light or power bank that is capable of (relatively) fast charging is only half the battle: you also need a charger that can give them the current that permits fast charging, and probably the right cable too. There is a confusion of standards around this. There's USB Quick Charge, which is a proprietary standard, and runs over USB-A ports, and USB Power Delivery, which comes from the USB standards body and runs over only USB-C ports (I think). Both work by delivering higher voltages. USB-PD has more voltages, and higher voltages, than Quick Charge. Some chargers support both.