Leaving a trainee something to eat (5)
I believe the answer is:
offal
'something to eat' is the definition.
(offal is a kind of food)
'leaving a trainee' is the wordplay.
'leaving' becomes 'off' (as in 'I'm off').
'trainee' becomes 'l' (as in an L-plate for a learner driver).
'off'+'a'+'l'='OFFAL'
(Other definitions for offal that I've seen before include "Liver or tongue, for example" , "Edible entrails of animals" , "Less valuable edible parts of animal" , "Internal organs of an animal used as food" , "Waste material" .)