The theme for November is blood, and you'll be forgiven for holding related events a day early, Halloween-themed activities are always very popular.
You could focus on anything to do with blood, what's in it, how it's made, or blood donation and transfusion. You could also organise events focusing on anaemias or leukaemia.
Why not organise an event to explain what different blood tests are for? Lab Tests Online-UK is a great resource for health professionals and patients, that explains why blood tests are performed and what the results mean.