It seems the common adventist practice is to bury the holy communion left overs. But considering what the wine and bread symbolise, (i.e. the blood and body of Christ), and that the above mentioned practice seems to lack sound biblical support, would it not be prudent to ensure that all the wine and bread is consume, somehow? (food for thought). Burying the wine and bread may have a totally different meaning to the interpretation of the ritual....
"And Moses said unto Aaron and to his sons, Boil the flesh at the door of the tabernacle of the congregation: and there eat it with the bread that is in the basket of consecrations, as I commanded, saying, Aaron and his sons shall eat it.
And that which remaineth of the flesh and of the bread shall ye burn with fire." Leviticus 8:21,32
"And Aaron and his sons shall eat the flesh of the ram, and the bread that is in the basket by the door of the tabernacle of the congregation.
And they shall eat those things wherewith the atonement was made, to consecrate and to sanctify them: but a stranger shall not eat thereof, because they are holy.
And if ought of the flesh of the consecrations, or of the bread, remain unto the morning, then thou shalt burn the remainder with fire: it shall not be eaten, because it is holy." Exodus 29:32-34