Assuming you have a light in the front so you can see the next most important is reflectors. All the posts here about reflectorized vests and straps are very good. The reflectors that came on your bike, especially those in the spokes and on the pedals, are very effective at attracting attention from an auto driver and identifying you as a moving bicycle. Nothing wrong with bike tail lights and blinkies but they are overpowered by car headlights and so don't show all that well.