Heavy drinker may flip coin for a prize (7)
I believe the answer is:
tosspot
'heavy drinker' is the definition.
'tosspot' can be an answer for 'drinker' (I have seen 'Habitual drinker' mean 'tosspot' so perhaps 'drinker' could also mean 'tosspot'). I am not sure about the 'heavy' bit.
'flip coin for a prize' is the wordplay.
'flip coin for' becomes 'toss' (I can't explain this - if you can you should believe this answer much more).
'a prize' becomes 'pot' (as in a jackpot).
'toss'+'pot'='TOSSPOT'
'may' is the link.
Can you help me to learn more?
(Other definitions for tosspot that I've seen before include "Drunk (informal)" , "Habitual drinker" , "Fool" , "One drunkard" , "supper, habitually" .)