In a pinch you can charge some lights while running them, via a USB battery pack. My low end helmet light can recharge and run simultaneously in high, low and flashing modes, and isn't picky about USB cord or battery. The Light & Motion Rando 500 can charge and run but only in low power and only with their proprietary USB cable.

Check with other light manufacturers to see whether their models can run and charge simultaneously. The main drawback will be compromised weather resistance with the USB port exposed (even with the USB cable plugged in), and securely mounting a USB battery, which can be bulky and heavy if it needs to last an entire day and night.

Ditto, taillights -- some can charge and run simultaneously, some can't.

For some all day/night casual group rides I've duct-taped one or more USB batteries to my top tube, stem or handlebar with cords running to the headlights. Not elegant but it works.