I'm not going to bother to try to look up the actual regulations right now,
but I seem to recall that kayaks, for whatever reason, are exempt from the red
and green light thing when out at night. We are required to carry a
"directional beam light," i.e., a flashlight, and that's about it. The purpose
of the directional beam light is to be able to use it to signal boats as to
your position in the event one looks like it is going to pass near you. Of
course that's in the US, I have no idea what the regulations are in
Switzerland.
When I am out paddling at night I usually tape a couple of chem lights to
the paddle shaft out towards the paddle blades to make myself more visible. You
want to avoid having any brighter lights on your boat as they will ruin your
night vision.
As for radar reflectors, it is my understanding (and once again I am going
from memory here, which is not as good as it used to be :-) that anything you
can carry in a kayak is, for the most part, useless. If you stick close to
shore then boat traffic should be not much of a concern.

Scott
So.Cal.