"Bottoms Up!" "Here's lookin at you!" "Mud in your eye!" "Cheers!'

Toast

Anyone who has ever drunk a toast to a friend's health or good fortune may have wondered how the word 'toast' came to designate a ceremony that involves no roasted slice of bread.
The custom of a host drinking to a friend's health originated with the Greeks, as early as the sixth century B.C., and for a highly practical reason: to assure guests that the wine they were about to drink was not poisoned. Spiking wine with poison had long been a preferred way to dispose of a political rival or suspected enemy, or to circumvent divorce. Thus a host sipped the first wine poured from a decanter, and satisfied of its safety, the guests raised their glasses and drank. This drinking in sequence-guests then host- came to symbolize a pledge of friendship and amity.
The Romans adopted the Greek penchant for poisoning and the custom of drinking as a pledge of friendship. The Roman custom of dropping a burnt piece of toast into a cup of wine is the origin of the verbal usage. It has been scientifically shown that charcoal can reduce a liquid's acidity, and that a blackened piece of bread added to an inferior, slightly vinegary wine can render it more mellow and palatable-something the Romans may have discovered for themselves.
In Summary: the Greeks drank to a friend's health: the Romans flavored the drink with toast; and in time the drink itself became a 'toast'.
From Extraordinary Origins of Everyday Things, Pg. 91