You need to be more specific here about what tradition you are questioning. Often the food was eaten by priests, or by the community as a whole, as a part of the ritual. The latter is true in Islam, where the meat is divided between the family, neighbors and people in need. Sometimes the sacrifices were/are burned, as in some Hindu rituals and as proscribed by some Biblical commands (but not all). It might be left out, and become food for animals, which is common in Tibetan Buddhism. I am less familiar with indigenous religions, so you will need to ask specifically to get a precise answer, but there are other practices such as burial of human sacrifices.