Personally, the highest priority for me on that list is dealing with the dark. For me, the reality is that my ride times are early in the morning, or late in the evening. Both propositions put me riding in the dark. Unfortunately, coupling that fact with the idea that we do not exactly ride in the most bicycling friendly city means that being seen on the road needs to be a priority for all of us.
So what can you do to be seen? Be bright! Be Visible! Do both of those things from all directions!
My rig consists of two primary lights, and some secondary things.
My lights are both from Cateye. I've had the rear so long that I really don't remember the model. I like it because it has some flashing modes that might set off a seizure in someone looking at it too long, and you can see it from the side. It also takes batteries you can get anywhere. The headlight is a Cateye Nima. Just came out and this is my first season with it. Its a new generation LED light which should have a lot of battery life to it. Again lots of flashing modes. Flashing gets attention.
Next up are the secondary things. Have you ever driven down the road, and then out of nowhere out steps someone in black jeans and a black or dark hoodie. Chances are, you felt that you almost ran them down, or might have. Think of the same situation with that person wearing a white hoodie - This time you would have seen them.
Same goes for your riding gear. Wear light color jersey's and jackets- Especially when riding in the dark or near dark. Light, bright colors allow you to be seen at a greater distance and in lower light conditions. All good things for cyclists. Your jersey or jacket also happens to be one of the highest points of your person while riding, again helping you become more visible at a distance.
What is the highest part of your person when riding? Your helmet. Black helmets not only are hot in the summer, but do you no favors in the dark. Wear a light colored helmet, and bonus if it happens to have reflective surfaces on it.
Do these things, and you'll have a much better ride and a much safer ride!