I discovered a rich tradition for such times in Judaism: http://www.shiva.com/learning-center/what-to-bring-or-send/food-condolence-baskets/ . I recently saw Victorian funeral biscuits in New York's Merchant's House Museum, http://merchantshouse.org/ ; they are discussed at http://historiccamdencounty.com/ccnews153.shtml (not a read for the squeamish). I've not found a scholarly resource on other cultures' mourning foods, though someone has tried to compile such a book...
So how about foods recommended to help with sadness in general? Here's what I've seen listed over the years as comforting to most humans, though I wonder how much it's affected by one's culture:
- a hot beverage you like
- fatty fish
- olive oil
- foods rich in folate/folic acid (rich sources include beans, dairy, fruit, nuts, tea, vegetables)
- if the mourning is from a traumatic event such as the unleashing of a foul misogynist: coriander, thyme, ginger, sage, oats, oranges