I consider myself to be a relatively safe driver, as I mentioned earlier this year. I'm engaged, relatively careful, and I consider myself to have pretty good driving skills. However, I may have been a hazard to other drivers because of the stuff I was carrying: mainly, vinyl stick-on logos and lightweight stuff in the back of a pickup truck.
The vinyl vehicle logos are meant to be slapped on once you arrive at the site. However, they don't stick so well once the vehicle has been covered with mud and/or road salt (nearly every day this winter). And at the end of a long week, it's easy to overlook and only remember you haven't taken the blasted thing off when you're 10 miles down the highway.
The stuff in the back of the pickup truck has a similar problem - you pack the pickup truck with all the big cases and boxes of supplies you need, and then at the end of the fieldwork you've shipped off the samples and what you have is a lot of trash to take back. Light, poorly-organized trash. So it's tempting to throw the trash bags in the back and head out... then you look in the rearview mirror and you see the trash bags levitating with every rut and wind gust.
I have managed to avoid striking anyone with flying chunks of vinyl. I may have been involved with an incident or two involving trash bags, but luckily, they were extremely light and I was on back roads without other traffic. Needless to say, I am now more careful to look over/pack whatever I'm driving before I head out.