As sawin said: nowadays most phones have a camera. I wouldn't ever recommend trying to take pictures while driving (unless you feared for your life too much to stop) but if you are forced to stop, get the video camera up and recording. That sort of evidence is much better than some witness who "thinks" they saw what happened. 911 recordings can be awfully helpful too.

Phone in one hand, gun in the other. If you cannot escape the situation and you fear for your life, aim well.