Kid not prepared to eat last of sister’s toast (5,2)

'toast' is the definition.
('drink to' can be a synonym of 'toast')

'kid not prepared to eat last of sister's' is the wordplay.
'prepared' indicates anagramming the letters.
'to eat' is an insertion indicator.
'last of' says to take the final letters.
The last letter of 'sister' is 'r'.
'kid'+'not'='kidnot'
'kidnot' with letters rearranged gives 'dinkto'.
'dinkto' placed around 'r' is 'DRINK TO'.