I second the recommendation for lights at night. However, some municipalities require reflectors at night, if you care about such regulations. Personally, I ditch the plastic reflectors because the tires I use have reflective sidewalls. You will find some controversy about the relative merits of sidewall reflectivity versus discrete rotating point reflectivity from a conspicuity point of view. I feel the rider's awareness of surrounding conditions more than compensates for any hypothetical differences in the effectiveness of different reflector types. I also wear reflective ankle straps on both legs; on the right for chain hygiene and the left for visibility in traffic (I'm in the US).
Steve