I think my favorite version of the tradition is the Greek idea that all the senses should be a part of the celebration (from the same link above):
In Ancient Greece, before the “Yimas” (to your health, or cheers), noise played a part in drinking as well. A myth I have heard is that wine, as well as all other things spiritual and beautiful, must appease and tempt each sense. The bouquet of the wine is for the nose, the colour for the eye, the body for taste and touch, and, of course, the clinking of the goblet for the ear. Ancient Greeks had other reasons for clinking cups: the first drink (the Proposis, or “the drink before”) was taken by the gods and not the mortals whom imbibed the rest of the drink. The Homeric ritual for this act involved rising to one’s feet and holding a drink in the right hand aloft, and then with both hands in air, praying “to the gods!” and then deliberately spilling some of the drink.
So I guess that last part is a bit like pouring out some for fallen “homies”