You can find black pudding in various guises all over the world but in the UK and Ireland it's essential pig's blood boiled up with a filller, usually oatmeal, and seasoning that congeals when it cools inside a skin and is then sliced and fried.

In Ireland and Scotland white pudding is also popular and consists of pork meat and fat, suet, bread, and oatmeal formed into the shape of a large sausage and then sliced and fried. No blood in this one.

They sound disgusting but actually when they're made well they taste superb.

Also, adding to the US v UK breakfast debate, I'm a sucker for toasted rye bread, egg whites and pink grapefruit juice all of which are difficult to find on UK breakfast menus.
So those, plus a few fried potatoes, are what I always eat stateside.

But in Greece, fresh local yoghurt covered in honey with a strong coffee is what gets me through the previous night's ouzo.