I like to take a few pictures each ride. At night this time of year I'll take pictures of Christmas lights. I tried keeping my phone out to take pictures last week and it conked out after an hour in the cold. I do like that I can grab the camera out of my back pocket and take pictures one handed on the fly even while wearing gloves.
For lights I wanted something with a ridiculously long runtime for brevets. I started with 1000 lumen Dinotte XML-3, then bought a newer one that is 2100 lumen, then sent the first one back for an upgrade to 2500. The newest one should run at about 700 lumens for 13 hours on a 6 cell battery.
Pedaling faster works for heating my core, but doesn't help with my hands / feet. With raynauds I need the heated stuff to keep my fingers / toes from going white and numb.