The RoadID site actually gives a good run down on what details are actually needed on any form of ID you may be carrying. Name (obviously) year of birth (don't need the exact date), city (don't need your full address), then a couple of contact numbers and then a list of any medical conditions that ambulance people should need to know about. They also give you a list of the know abreviations for certain conditions.
You don't need your full address or date of birth as that isn't needed for treating you on the side of the road, an approximate idea of age though from year of birth is sufficient. Your name, city and contact numbers will be more than enough for them to figure out exactly who you are when they get you to hospital.
The marshals might not have the right to stop cars, but cars have no right to run over runners either.
Knowing where they are on the course is handy, and if there are gaps between the runners then have their arm out pointing in the direction we have to go nice and early helps. Make sure that they are stood in the right spot on tight turns or where there are a few different options of paths to take so that we don't have to think too much in our confused racing state of mind.