What you might make on a good day? (3)
I believe the answer is:
hay
'what you might' is the definition.
I can't tell whether this defines the answer.
'on a good day?' is the wordplay.
'on' means one lot of letters goes inside another (as in clothing 'on' a person).
'good day?' becomes 'hy' (I can't justify this - if you can you should give a lot more credence to this answer).
'a' put inside 'hy' is 'HAY'.
'make' acts as a link.
Can you help me to learn more?
(Other definitions for hay that I've seen before include "Meadow crop" , "It is to be made while the sun shines" , "Straw" , "Welsh festival" , "basic bedding" .)