WOW that puts the "Fear of Driver" in me. I have mostly relied on eye contact but will incorporate vrkelley's suggestion on watching wheels. I have also started to be a bit more assertive also by pointing my intended direction which seems to get noticed.

Your Pannier physics lesson reminded me of a crash I had years ago when I hit a pot-hole and flipped over the bars.... Somehow me and the bike (old 10-speed) danced in the air and when we hit the ground my FOREARM was between the Fork and the Rim. Yes there was major compression which forced the perimedics to cut my beloved steed to release me.