Not just carry, but use, in the event of an incident. Most cars probably have a triangle etc in the back? but in Germany at least you are expected to use it (by law).
Hi viz, 1st aid kit, triangle, spare bulbs (+ screwdriver or whatever tools you need to change them!), all cost peanuts so may as well have them anyway (except at Dover, where they’ll cost 4x the price in Halfrauds).
Headlights vary. Cant put deflectors on Xenon ones afaik. Mine are impossible to fit, so I just don’t drive at night.