Ran the calculations some time ago, and donating a half liter of blood gets rid of about 500kcal, which I can easily manage to do in under half hour not counting the paperwork. I think the only more calorie-consuming activity I can think of is liposuction or mutilation of body parts. Not that I recommend either, just a random thought.
The red cross has been messing around with their vendors recently and the new granola bars and cheez-its are totally shit now. Not even the cookies are good.