Hi-viz clothing is your friend in daylight. Reflective gear does no good whatsoever unless its dark/dim and drivers have their headlights on (and many do not even when it's nearly dark outside). I have a collection of neon yellow jerseys, jackets and vests that I almost always wear when commuting. I was convinced of their effectiveness when I spotted a jogger 1/2-mile ahead of me during early morning hours. I also run my head and taillights during the day. My taillight is a super bright Dinotte 140 that is powerful enough to be visible in daylight, and my headlight is even brighter. Last but not least, you always need to ride defensively and assume that drivers don't see you, no matter how brightly lit and dressed you are.