Supper often late initially stops one rewarding waiter (7)
I believe the answer is:
tippler
'supper often' is the definition.
(someone who often drinks alcohol)
'late initially stops one rewarding waiter' is the wordplay.
'initially' says to take the initial letters.
'stops' is an insertion indicator (stopping can mean blocking a gap).
'one rewarding waiter' becomes 'tipper' (someone giving a tip).
The initial letter of 'late' is 'l'.
'l' going inside 'tipper' is 'TIPPLER'.
(Other definitions for tippler that I've seen before include "One habitually drinking" , "Heavy drinker" , "Drunk" , "Person who drinks constantly in small amounts" , "Habitual drinker" .)