“In Russia, when someone dies, you leave an empty spot at the table. Then you pour one shot glass of vodka and put a piece of bread over the glass. This makes it like they’re still with you and you’re still making room for them in your home.”

Like the informant said, after death, the deceased person still is a part of the lives of the living. The people remember the person through leaving food, which is inherently is meant to sustain you physically, though in case it sustains the person spiritually. According to PBS, the bread on top of the glass is black, and its a ‘reversal of the traditional Russian custom of breaking black bread when meeting someone for the first time.’ Therefore, though the living are temporarily memorializing the dead with the food, they are also saying goodbye for the last time.

Citation: http://www.pbs.org/wnet/onourownterms/articles/cultural.html