Q? for the rescue unit peeps

[Bodysnatcher]

Debate raging on Steve's Yahoo board about the usefulness of embroidered Blood Groups.
As an ex blood transfusion worker, (grown up & into transplants now, hence the nik) I reckon it's ******. We'd have been done for professional misconduct at the least if we paid any attention to that sort of thing.
Steve from Goodwood reckons that in his accident having his blood group on him helped save his life.

So, to the point, how much blood does a unit carry and what group/rhesus is it?
or is it all just stuff like Dextran or Hemacell?