My father used to be fond of pickled cow stomach, the part that looks like over sized honeycomb, called tripe. I would eat it, rather than offend him, but I have never bought any.
Haggis I have been told is a variety of bits of heart, lung,liver, kidneys etc with oatmeal and other vegetables and seasonings cooked in a sheep stomach. I have never had any, and would not much care to partake of it, but the Yankee in me approves of not wasting any food. "Wilful waste brings woeful want."