A coworker did not clean his work area before going home. This could cause an accident, so you quickly clean up. The next day you see the coworker. What would you be most and least likely to do?

The first option "tell him he should be more careful because his work area could result in an accident"

Explanation: The first option is the best one. Talk direct with your coworkers and express your concerns with them. Only if this has no effect you should talk with your supervisor, because if you do it at the start, the work environment may suffer from it.  

So if this is the first time that this happens, You should show confidence in your coworker and talk to him first.