Iodine. I know it can be used to treat reptiles, but is it standard fare for humans? [Me = someone who knows nothing about first aid]
If so - does it smell or sting or stain skin?
On a related note - what would go in a First Aid kit in America and how much of it would go in? (Just in case it's different from everywhere else. Not that I even know the contents of a British one, but still.)