Willing worker's average beer supply (5,6)
I believe the answer is:
eager beaver
'willing worker's' is the definition.
'eager beaver' can be an answer for 'worker's' (eager beaver is a kind of worker). I am unsure of the 'willing' bit.
'average beer supply' is the wordplay.
'supply' indicates an anagram (in a supple way).
'average'+'beer'='averagebeer'
'averagebeer' is an anagram of 'EAGER BEAVER'.
Can you help me to learn more?
(Other definitions for eager beaver that I've seen before include "very keen type" , "Diligent worker" , "keen customer" , "Enthusiast - zealous person - one too eager to work" , "Very keen individual" .)